Terminology
This appendix summarizes the IBM Spectrum Virtualize and IBM SAN Volume Controller (SVC) terms that are commonly used in this book.
To see the complete set of terms that relate to the IBM SAN Volume Controller, see the Glossary section of IBM Knowledge Center for SVC, which is available at:
Commonly encountered terms
This book uses the common IBM Spectrum Virtualize and SVC terminology listed in this section.
Array
An ordered collection, or group, of physical devices (disk drive modules) that are used to define logical volumes or devices. An array is a group of drives designated to be managed with a Redundant Array of Independent Disks (RAID).
Asymmetric virtualization
Asymmetric virtualization is a virtualization technique in which the virtualization engine is outside the data path and performs a metadata-style service. The metadata server contains all the mapping and locking tables, and the storage devices contain only data. See also “Symmetric virtualization” on page 797.
Asynchronous replication
Asynchronous replication is a type of replication in which control is given back to the application as soon as the write operation is made to the source volume. Later, the write operation is made to the target volume. See also “Synchronous replication” on page 797.
Automatic data placement mode
Automatic data placement mode is an Easy Tier operating mode in which the host activity on all the volume extents in a pool are “measured,” a migration plan is created, and then automatic extent migration is performed.
Back end
Caching I/O Group
The caching I/O Group is the I/O Group in the system that performs the cache function for a volume.
Call home
Call home is a communication link that is established between a product and a service provider. The product can use this link to call IBM or another service provider when the product requires service. With access to the machine, service personnel can perform service tasks, such as viewing error and problem logs or initiating trace and dump retrievals.
Canister
A canister is a single processing unit within a storage system.
Capacity licensing
Capacity licensing is a licensing model that licenses features with a price-per-terabyte model. Licensed features are FlashCopy, Metro Mirror, Global Mirror, and virtualization. See also “FlashCopy” on page 787, “Metro Mirror” on page 791, and “Virtualization” on page 798.
Chain
A set of enclosures that are attached to provide redundant access to the drives inside the enclosures. Each control enclosure can have one or more chains.
Challenge Handshake Authentication Protocol
Challenge Handshake Authentication Protocol (CHAP) is an authentication protocol that protects against eavesdropping by encrypting the user name and password.
Channel extender
A channel extender is a device that is used for long-distance communication that connects other storage area network (SAN) fabric components. Generally, channel extenders can involve protocol conversion to asynchronous transfer mode (ATM), Internet Protocol (IP), or another long-distance communication protocol.
Child pool
Administrators can use child pools to control capacity allocation for volumes that are used for specific purposes. Rather than being created directly from managed disks (MDisks), child pools are created from existing capacity that is allocated to a parent pool. As with parent pools, volumes can be created that specifically use the capacity that is allocated to the child pool. Child pools are similar to parent pools with similar properties. Child pools can be used for volume copy operation. Also, see “Parent pool” on page 792.
Cloud Container
Cloud Container is a virtual object that include all of the elements, components, or data that are common to a specific application or data.
Cloud Provider
Cloud provider is the company or organization that provide off- and on-premises cloud services such as storage, server, network, and so on. IBM Spectrum Virtualize has built-in software capabilities to interact with Cloud Providers such as IBM Cloud, Amazon S3, and deployments of OpenStack Swift.
Cloud Tenant
Cloud Tenant is a group or an instance that provides common access with the specific privileges to an object, software, or data source.
Clustered system (SVC)
A clustered system, which was known as a cluster, is a group of up to eight SVC nodes that presents a single configuration, management, and service interface to the user.
Cold extent
A cold extent is an extent of a volume that does not get any performance benefit if it is moved from a hard disk drive (HDD) to a Flash disk. A cold extent also refers to an extent that needs to be migrated onto an HDD if it is on a Flash disk drive.
Compression
Compression is a function that removes repetitive characters, spaces, strings of characters, or binary data from the data that is being processed and replaces characters with control characters. Compression reduces the amount of storage space that is required for data.
Compression accelerator
A compression accelerator is hardware onto which the work of compression is offloaded from the microprocessor.
Configuration node
While the cluster is operational, a single node in the cluster is appointed to provide configuration and service functions over the network interface. This node is termed the configuration node. This configuration node manages the data that describes the clustered-system configuration and provides a focal point for configuration commands. If the configuration node fails, another node in the cluster transparently assumes that role.
Consistency Group
A Consistency Group is a group of copy relationships between virtual volumes or data sets that are maintained with the same time reference so that all copies are consistent in time. A Consistency Group can be managed as a single entity.
Container
A container is a software object that holds or organizes other software objects or entities.
Contingency capacity
For thin-provisioned volumes that are configured to automatically expand, the unused real capacity that is maintained. For thin-provisioned volumes that are not configured to automatically expand, the difference between the used capacity and the new real capacity.
Copied state
Copied is a FlashCopy state that indicates that a copy was triggered after the copy relationship was created. The Copied state indicates that the copy process is complete and the target disk has no further dependency on the source disk. The time of the last trigger event is normally displayed with this status.
Counterpart SAN
A counterpart SAN is a non-redundant portion of a redundant SAN. A counterpart SAN provides all of the connectivity of the redundant SAN, but without the 100% redundancy. SVC nodes are typically connected to a “redundant SAN” that is made up of two counterpart SANs. A counterpart SAN is often called a SAN fabric.
Cross-volume consistency
A consistency group property that ensures consistency between volumes when an application issues dependent write operations that span multiple volumes.
Data consistency
Data consistency is a characteristic of the data at the target site where the dependent write order is maintained to ensure the recoverability of applications.
Data encryption key
The data encryption key is used to encrypt data. It is created automatically when an encrypted object, such as an array, a pool, or a child pool, is created. It is stored in secure memory and it cannot be viewed or changed. The data encryption key is encrypted using the master access key.
Data migration
Data migration is the movement of data from one physical location to another physical location without the disruption of application I/O operations.
Dependent write operation
A write operation that must be applied in the correct order to maintain cross-volume consistency.
Directed maintenance procedure
The fix procedures, which are also known as directed maintenance procedures (DMPs), ensure that you fix any outstanding errors in the error log. To fix errors, from the Monitoring pane, click Events. The Next Recommended Action is displayed at the top of the Events window. Select Run This Fix Procedure and follow the instructions.
Discovery
The automatic detection of a network topology change, for example, new and deleted nodes or links.
Disk tier
MDisks (logical unit numbers (LUNs)) that are presented to the SVC cluster likely have different performance attributes because of the type of disk or RAID array on which they are installed. The MDisks can be on 15,000 revolutions per minute (RPM) Fibre Channel (FC) or serial-attached SCSI (SAS) disk, Nearline SAS, or Serial Advanced Technology Attachment (SATA), or even Flash Disks. Therefore, a storage tier attribute is assigned to each MDisk and the default is generic_hdd. SVC 6.1 introduced a new disk tier attribute for Flash Disk, which is known as generic_ssd.
Distributed RAID or DRAID
An alternative RAID scheme where the number of drives that are used to store the array can be greater than the equivalent, typical RAID scheme. The same data stripes are distributed across a greater number of drives, which increases the opportunity for parallel I/O and hence improves performance of the array. See also “Rebuild area” on page 794.
Easy Tier
Easy Tier is a volume performance function within the SVC that provides automatic data placement of a volume’s extents in a multitiered storage pool. The pool normally contains a mix of Flash Disks and HDDs. Easy Tier measures host I/O activity on the volume’s extents and migrates hot extents onto the Flash Disks to ensure the maximum performance.
Encryption key
The encryption key, also known as the master access key, is created and stored on USB flash drives or on a key server when encryption is enabled. The master access key is used to decrypt the data encryption key.
Encryption key server
An internal or external system that receives and then serves existing encryption keys or certificates to a storage system.
Encryption of data at rest
Encryption of data at rest is the inactive encryption data that is stored physically on the storage system.
Enhanced Stretched Systems
A stretched system is an extended high availability (HA) method that is supported by the SVC to enable I/O operations to continue after the loss of half of the system. Enhanced Stretched Systems provide the following primary benefits. In addition to the automatic failover that occurs when a site fails in a standard stretched system configuration, an Enhanced Stretched System provides a manual override that can be used to select which of two sites continues operation.
Enhanced Stretched Systems intelligently route I/O traffic between nodes and controllers to reduce the amount of I/O traffic between sites, and to minimize the effect on host application I/O latency. Enhanced Stretched Systems include an implementation of additional policing rules to ensure that the correct configuration of a standard stretched system is used.
Evaluation mode
The evaluation mode is an Easy Tier operating mode in which the host activity on all the volume extents in a pool are “measured” only. No automatic extent migration is performed.
Event (error)
An event is an occurrence of significance to a task or system. Events can include the completion or failure of an operation, user action, or a change in the state of a process. Before SVC V6.1, this situation was known as an error.
Event code
An event code is a value that is used to identify an event condition to a user. This value might map to one or more event IDs or to values that are presented on the service window. This value is used to report error conditions to IBM and to provide an entry point into the service guide.
Event ID
An event ID is a value that is used to identify a unique error condition that was detected by the SVC. An event ID is used internally in the cluster to identify the error.
Excluded condition
The excluded condition is a status condition. It describes an MDisk that the SVC decided is no longer sufficiently reliable to be managed by the cluster. The user must issue a command to include the MDisk in the cluster-managed storage.
Extent
An extent is a fixed-size unit of data that is used to manage the mapping of data between MDisks and volumes. The size of the extent can range from 16 MB - 8 GB.
External storage
External storage refers to MDisks that are SCSI logical units that are presented by storage systems that are attached to and managed by the clustered system.
Failback
Failback is the restoration of an appliance to its initial configuration after the detection and repair of a failed network or component.
Failover
Failover is an automatic operation that switches to a redundant or standby system or node in a software, hardware, or network interruption. See also Failback.
Feature activation code
An alphanumeric code that activates a licensed function on a product.
Fibre Channel port logins
FC port logins refer to the number of hosts that can see any one SVC node port. The SVC has a maximum limit per node port of FC logins that are allowed.
Field-replaceable unit
Field-replaceable units (FRUs) are individual parts that are replaced entirely when any one of the unit’s components fails. They are held as spares by the IBM service organization.
FlashCopy
FlashCopy refers to a point-in-time copy where a virtual copy of a volume is created. The target volume maintains the contents of the volume at the point in time when the copy was established. Any subsequent write operations to the source volume are not reflected on the target volume.
FlashCopy mapping
A FlashCopy mapping is a continuous space on a direct-access storage volume that is occupied by or reserved for a particular data set, data space, or file.
FlashCopy relationship
See FlashCopy mapping.
FlashCopy service
FlashCopy service is a copy service that duplicates the contents of a source volume on a target volume. In the process, the original contents of the target volume are lost. See also “Point-in-time copy” on page 792.
Flash drive
A data storage device that uses solid-state memory to store persistent data.
Flash module
A modular hardware unit that contains flash memory, one or more flash controllers, and associated electronics.
Front end and back end
The SVC takes MDisks to create pools of capacity from which volumes are created and presented to application servers (hosts). The volumes that are presented to the hosts are in the front end of the SVC.
Global Mirror
Global Mirror (GM) is a method of asynchronous replication that maintains data consistency across multiple volumes within or across multiple systems. Global Mirror is generally used where distances between the source site and target site cause increased latency beyond what the application can accept.
Global Mirror with change volumes
Change volumes are used to record changes to the primary and secondary volumes of a remote copy relationship. A FlashCopy mapping exists between a primary and its change volume, and a secondary and its change volume.
Grain
A grain is the unit of data that is represented by a single bit in a FlashCopy bitmap (64 KiB or 256 KiB) in the SVC. A grain is also the unit to extend the real size of a thin-provisioned volume (32 KiB, 64 KiB, 128 KiB, or 256 KiB).
Hop
One segment of a transmission path between adjacent nodes in a routed network.
Host bus adapter
A host bus adapter (HBA) is an interface card that connects a server to the SAN environment through its internal bus system, for example, PCI Express. Typically it is referred to the Fibre Channel adapters.
Host ID
A host ID is a numeric identifier that is assigned to a group of host FC ports or Internet Small Computer System Interface (iSCSI) host names for LUN mapping. For each host ID, SCSI IDs are mapped to volumes separately. The intent is to have a one-to-one relationship between hosts and host IDs, although this relationship cannot be policed.
Host mapping
Host mapping refers to the process of controlling which hosts have access to specific volumes within a cluster. Host mapping is equivalent to LUN masking. Before SVC V6.1, this process was known as VDisk-to-host mapping.
Hot extent
A hot extent is a frequently accessed volume extent that gets a performance benefit if it is moved from an HDD onto a Flash Disk.
Hot Spare Node
Hot Spare Node is an online SVC node defined in a cluster, but not in any IO group. During a failure of any of online nodes in any IO group of cluster, it is automatically swapped with this spare node. After the recovery of an original node has finished, the spare node returns to the standby spare status.
HyperSwap
Pertaining to a function that provides continuous, transparent availability against storage errors and site failures, and is based on synchronous replication.
Image mode
Image mode is an access mode that establishes a one-to-one mapping of extents in the storage pool (existing LUN or (image mode) MDisk) with the extents in the volume.
Image volume
An image volume is a volume in which a direct block-for-block translation exists from the MDisk to the volume.
I/O Group
Each pair of SVC cluster nodes is known as an input/output (I/O) Group. An I/O Group has a set of volumes that are associated with it that are presented to host systems. Each SVC node is associated with exactly one I/O Group. The nodes in an I/O Group provide a failover and failback function for each other.
Internal storage
Internal storage refers to an array of MDisks and drives that are held in enclosures and in nodes that are part of the SVC cluster.
Internet Small Computer System Interface qualified name
Internet Small Computer System Interface (iSCSI) qualified name (IQN) refers to special names that identify both iSCSI initiators and targets. IQN is one of the three name formats that is provided by iSCSI. The IQN format is iqn.<yyyy-mm>.<reversed domain name>. For example, the default for an SVC node can be in the following format:
iqn.1986-03.com.ibm:2145.<clustername>.<nodename>
Internet storage name service
The Internet Storage Name Service (iSNS) protocol that is used by a host system to manage iSCSI targets and the automated iSCSI discovery, management, and configuration of iSCSI and FC devices. It was defined in Request for Comments (RFC) 4171.
Inter-switch link hop
An inter-switch link (ISL) is a connection between two switches and counted as one ISL hop. The number of hops is always counted on the shortest route between two N-ports (device connections). In an SVC environment, the number of ISL hops is counted on the shortest route between the pair of nodes that are farthest apart. The SVC supports a maximum of three ISL hops.
Input/output group
A collection of volumes and node relationships that present a common interface to host systems. Each pair of nodes is known as an I/O group.
iSCSI initiator
An initiator functions as an iSCSI client. An initiator typically serves the same purpose to a computer as a SCSI bus adapter would, except that, instead of physically cabling SCSI devices (like hard drives and tape changers), an iSCSI initiator sends SCSI commands over an IP network.
iSCSI session
The interaction (conversation) between an iSCSI Initiator and an iSCSI Target.
iSCSI target
An iSCSI target is a storage resource located on an iSCSI server.
Latency
The time interval between the initiation of a send operation by a source task and the completion of the matching receive operation by the target task. More generally, latency is the time between a task initiating data transfer and the time that transfer is recognized as complete at the data destination.
Least recently used
Least recently used (LRU) pertains to an algorithm used to identify and make available the cache space that contains the data that was least recently used.
Licensed capacity
The amount of capacity on a storage system that a user is entitled to configure.
License key
An alphanumeric code that activates a licensed function on a product.
License key file
A file that contains one or more licensed keys.
Lightweight Directory Access Protocol
Lightweight Directory Access Protocol (LDAP) is an open protocol that uses TCP/IP to provide access to directories that support an X.500 model. It does not incur the resource requirements of the more complex X.500 directory access protocol (DAP). For example, LDAP can be used to locate people, organizations, and other resources in an Internet or intranet directory.
Local and remote fabric interconnect
The local fabric interconnect and the remote fabric interconnect are the SAN components that are used to connect the local and remote fabrics. Depending on the distance between the two fabrics, they can be single-mode optical fibers that are driven by long wave (LW) gigabit interface converters (GBICs) or Small Form-factor Pluggables (SFPs), or more sophisticated components, such as channel extenders or special SFP modules that are used to extend the distance between SAN components.
Local fabric
The local fabric is composed of SAN components (switches, cables, and so on) that connect the components (nodes, hosts, and switches) of the local cluster together.
Logical unit and logical unit number
The logical unit (LU) is defined by the SCSI standards as a LUN. LUN is an abbreviation for an entity that exhibits disk-like behavior, such as a volume or an MDisk.
Machine signature
A string of characters that identifies a system. A machine signature might be required to obtain a license key.
Managed disk
An MDisk is a SCSI disk that is presented by a RAID controller and managed by the SVC. The MDisk is not visible to host systems on the SAN.
Managed disk group (storage pool)
Metro Global Mirror
Metro Mirror Global is a cascaded solution where Metro Mirror synchronously copies data to the target site. This Metro Mirror target is the source volume for Global Mirror that asynchronously copies data to a third site. This solution has the potential to provide disaster recovery with no data loss at Global Mirror distances when the intermediate site does not participate in the disaster that occurs at the production site.
Metro Mirror
Metro Mirror (MM) is a method of synchronous replication that maintains data consistency across multiple volumes within the system. Metro Mirror is generally used when the write latency that is caused by the distance between the source site and target site is acceptable to application performance.
Mirrored volume
A mirrored volume is a single virtual volume that has two physical volume copies. The primary physical copy is known within the SVC as copy 0 and the secondary copy is known within the SVC as copy 1.
Node
An SVC node is a hardware entity that provides virtualization, cache, and copy services for the cluster. The SVC nodes are deployed in pairs that are called I/O Groups. One node in a clustered system is designated as the configuration node.
Node canister
A node canister is a hardware unit that includes the node hardware, fabric and service interfaces, and serial-attached SCSI (SAS) expansion ports. Node canisters are specifically recognized on IBM Storwize products. In SVC, all these components are spread within the whole system chassis, so we usually do not consider node canisters in SVC, but just the node as a whole.
Node rescue
The process by which a node that has no valid software installed on its hard disk drive can copy software from another node connected to the same Fibre Channel fabric.
NPIV
N_Port ID Virtualization (NPIV) is a Fibre Channel feature whereby multiple Fibre Channel node port (N_Port) IDs can share a single physical N_Port.
Object Storage
Object storage is a general term that refers to the entity in which Cloud Object Storage organizes, manages, and stores with units of storage, or just objects.
Oversubscription
Oversubscription refers to the ratio of the sum of the traffic on the initiator N-port connections to the traffic on the most heavily loaded ISLs, where more than one connection is used between these switches. Oversubscription assumes a symmetrical network, and a specific workload that is applied equally from all initiators and sent equally to all targets. A symmetrical network means that all the initiators are connected at the same level, and all the controllers are connected at the same level.
Parent pool
Parent pools receive their capacity from MDisks. All MDisks in a pool are split into extents of the same size. Volumes are created from the extents that are available in the pool. You can add MDisks to a pool at any time either to increase the number of extents that are available for new volume copies or to expand existing volume copies. The system automatically balances volume extents between the MDisks to provide the best performance to the volumes.
Partnership
In Metro Mirror or Global Mirror operations, the relationship between two clustered systems. In a clustered-system partnership, one system is defined as the local system and the other system as the remote system.
Point-in-time copy
A point-in-time copy is an instantaneous copy that the FlashCopy service makes of the source volume. See also “FlashCopy service” on page 788.
Preparing phase
Before you start the FlashCopy process, you must prepare a FlashCopy mapping. The preparing phase flushes a volume’s data from cache in preparation for the FlashCopy operation.
Primary volume
In a stand-alone Metro Mirror or Global Mirror relationship, the target of write operations that are issued by the host application.
Private fabric
Configure one SAN per fabric so that it is dedicated for node-to-node communication. This SAN is referred to as a private SAN.
Public fabric
Configure one SAN per fabric so that it is dedicated for host attachment, storage system attachment, and remote copy operations. This SAN is referred to as a public SAN. You can configure the public SAN to allow SVC node-to-node communication also. You can optionally use the -localportfcmask parameter of the chsystem command to constrain the node-to-node communication to use only the private SAN.
Quorum disk
A disk that contains a reserved area that is used exclusively for system management. The quorum disk is accessed when it is necessary to determine which half of the clustered system continues to read and write data. Quorum disks can either be MDisks or drives.
Quorum index
The quorum index is the pointer that indicates the order that is used to resolve a tie. Nodes attempt to lock the first quorum disk (index 0), followed by the next disk (index 1), and finally the last disk (index 2). The tie is broken by the node that locks them first.
RACE engine
The RACE engine compresses data on volumes in real time with minimal effect on performance. See “Compression” on page 784 or “Real-time Compression” on page 793.
Real capacity
Real capacity is the amount of storage that is allocated to a volume copy from a storage pool.
Real-time Compression
Real-time Compression is an IBM integrated software function for storage space efficiency. The RACE engine compresses data on volumes in real time with minimal effect on performance.
Redundant Array of Independent Disks
RAID refers to two or more physical disk drives that are combined in an array in a certain way, which incorporates a RAID level for failure protection or better performance. The most common RAID levels are 0, 1, 5, 6, and 10. Some storage administrators refer to the RAID group as Traditional RAID (TRAID).
RAID 0
RAID 0 is a data striping technique that is used across an array that provides no data protection.
RAID 1
RAID 1 is a mirroring technique that is used on a storage array in which two or more identical copies of data are maintained on separate mirrored disks.
RAID 10
RAID 10 is a combination of a RAID 0 stripe that is mirrored (RAID 1). Therefore, two identical copies of striped data exist, with no parity.
RAID 5
RAID 5 is an array that has a data stripe, which includes a single logical parity drive. The parity check data is distributed across all the disks of the array.
RAID 6
RAID 6 is a RAID level that has two logical parity drives per stripe, which are calculated with different algorithms. Therefore, this level can continue to process read and write requests to all of the array’s virtual disks in the presence of two concurrent disk failures.
Read intensive drives
The read intensive flash drives that are available on Storwize V7000 Gen2, Storwize V5000 Gen2, and SAN Volume Controller 2145-DH8, SV1, and 24F enclosures are one Drive Write Per Day (DWPD) read Intensive drives.
Rebuild area
Reserved capacity that is distributed across all drives in a redundant array of drives. If a drive in the array fails, the lost array data is systematically restored into the reserved capacity, returning redundancy to the array. The duration of the restoration process is minimized because all drive members simultaneously participate in restoring the data. See also “Distributed RAID or DRAID” on page 785.
Redundant storage area network
A redundant SAN is a SAN configuration in which there is no single point of failure (SPOF). Therefore, data traffic continues no matter what component fails. Connectivity between the devices within the SAN is maintained (although possibly with degraded performance) when an error occurs. A redundant SAN design is normally achieved by splitting the SAN into two independent counterpart SANs (two SAN fabrics). In this configuration, if one path of the counterpart SAN is destroyed, the other counterpart SAN path keeps functioning.
Relationship
In Metro Mirror or Global Mirror, a relationship is the association between a master volume and an auxiliary volume. These volumes also have the attributes of a primary or secondary volume.
Reliability, availability, and serviceability
Reliability, availability, and serviceability (RAS) are a combination of design methodologies, system policies, and intrinsic capabilities that, when taken together, balance improved hardware availability with the costs that are required to achieve it.
Reliability is the degree to which the hardware remains free of faults. Availability is the ability of the system to continue operating despite predicted or experienced faults. Serviceability is how efficiently and nondisruptively broken hardware can be fixed.
Remote fabric
The remote fabric is composed of SAN components (switches, cables, and so on) that connect the components (nodes, hosts, and switches) of the remote cluster together. Significant distances can exist between the components in the local cluster and those components in the remote cluster.
Remote Support Server and Client
Remote Support Client is a software toolkit that resides in the SVC and opens a secured tunnel to the Remote Support Server. Remote Support Server resides in the IBM network and collects key health check and troubleshooting information that is required by IBM Support personnel.
SAN Volume Controller
The IBM SAN Volume Controller (SVC) is an appliance that is designed for attachment to various host computer systems. The IBM Spectrum Virtualize is a software engine of SVC that performs block-level virtualization of disk storage.
Secondary volume
Pertinent to remote copy, the volume in a relationship that contains a copy of data written by the host application to the primary volume. See also “Relationship” on page 795.
Secure Sockets Layer certificate
Secure Sockets Layer (SSL) is the standard security technology for establishing an encrypted link between a web server and a browser. This link ensures that all data passed between the web server and browsers remain private. To be able to create an SSL connection, a web server requires an SSL Certificate.
Security Key Lifecycle Manager
Security Key Lifecycle Manager (SKLM) centralizes, simplifies, and automates the encryption key management process to help minimize risk and reduce operational costs of encryption key management.
Serial-attached SCSI
SAS is a method that is used in accessing computer peripheral devices that employs a serial (one bit at a time) means of digital data transfer over thin cables. The method is specified in the American National Standard Institute standard called SAS. In the business enterprise, SAS is useful for access to mass storage devices, particularly external hard disk drives.
Service Location Protocol
Service Location Protocol (SLP) is an Internet service discovery protocol that enables computers and other devices to find services in a local area network (LAN) without prior configuration. It was defined in the request for change (RFC) 2608.
Small Computer System Interface
Small Computer System Interface (SCSI) is an ANSI-standard electronic interface with which personal computers can communicate with peripheral hardware, such as disk drives, tape drives, CD-ROM drives, printers, and scanners, faster and more flexibly than with previous interfaces.
Snapshot
A snapshot is an image backup type that consists of a point-in-time view of a volume.
Solid-state disk
A solid-state disk (SSD) or Flash Disk is a disk that is made from solid-state memory and therefore has no moving parts. Most SSDs use NAND-based flash memory technology. It is defined to the SVC as a disk tier generic_ssd.
Space efficient
Spare
An extra storage component, such as a drive or tape, that is predesignated for use as a replacement for a failed component.
Spare goal
The optimal number of spares that are needed to protect the drives in the array from failures. The system logs a warning event when the number of spares that protect the array drops below this number.
Space-efficient virtual disk
For more information about a space-efficient virtual disk (VDisk), see “Thin-provisioned volume” on page 797.
Stand-alone relationship
In FlashCopy, Metro Mirror, and Global Mirror, relationships that do not belong to a consistency group and that have a null consistency-group attribute.
Statesave
Binary data collection that is used for problem determination by service support.
Storage area network
A SAN is a dedicated storage network that is tailored to a specific environment, which combines servers, systems, storage products, networking products, software, and services.
Storage Capacity Unit
The IBM SVC software licensing metric is being changed to Differential Licensing to help align the cost of SVC licenses with customer use cases. In Differential Licensing, licenses changes from per terabyte to per storage capacity unit (SCU).
Storage pool (managed disk group)
A storage pool is a collection of storage capacity, which is made up of MDisks, that provides the pool of storage capacity for a specific set of volumes. A storage pool can contain more than one tier of disk, which is known as a multitier storage pool and a prerequisite of Easy Tier automatic data placement. Before SVC V6.1, this storage pool was known as a managed disk group (MDG).
Stretched system
A stretched system is an extended high availability (HA) method that is supported by SVC to enable I/O operations to continue after the loss of half of the system. A stretched system is also sometimes referred to as a split system. One half of the system and I/O Group is usually in a geographically distant location from the other, often 10 kilometers (6.2 miles) or more. A third site is required to host a storage system that provides a quorum disk.
Striped
Pertaining to a volume that is created from multiple MDisks that are in the storage pool. Extents are allocated on the MDisks in the order specified.
Support Assistance
A function that is used to provide support personnel remote access to the system to perform troubleshooting and maintenance tasks.
Symmetric virtualization
Symmetric virtualization is a virtualization technique in which the physical storage, in the form of a RAID, is split into smaller chunks of storage known as extents. These extents are then concatenated, by using various policies, to make volumes. See also “Asymmetric virtualization” on page 782.
Synchronous replication
Synchronous replication is a type of replication in which the application write operation is made to both the source volume and target volume before control is given back to the application. See also “Asynchronous replication” on page 782.
Thin-provisioned volume
A thin-provisioned volume is a volume that allocates storage when data is written to it.
Thin provisioning
Thin provisioning refers to the ability to define storage, usually a storage pool or volume, with a “logical” capacity size that is larger than the actual physical capacity that is assigned to that pool or volume. Therefore, a thin-provisioned volume is a volume with a virtual capacity that differs from its real capacity. Before SVC V6.1, this thin-provisioned volume was known as space efficient.
Throttles
Throttling is a mechanism to control the amount of resources that are used when the system is processing I/Os on supported objects. The system supports throttles on hosts, host clusters, volumes, copy offload operations, and storage pools. If a throttle limit is defined, the system either processes the I/O for that object, or delays the processing of the I/O to free resources for more critical I/O operations.
Transparent Cloud Tiering
Transparent Cloud Tiering is a separately installable feature of IBM Spectrum Scale™ that provides a native cloud storage tier.
T10 DIF
T10 DIF is a Data Integrity Field (DIF) extension to SCSI to enable end-to-end protection of data from host application to physical media.
Unique identifier
A unique identifier (UID) is an identifier that is assigned to storage-system logical units when they are created. It is used to identify the logical unit regardless of the LUN, the status of the logical unit, or whether alternate paths exist to the same device. Typically, a UID is used only once.
Virtualization
In the storage industry, virtualization is a concept in which a pool of storage is created that contains several storage systems. Storage systems from various vendors can be used. The pool can be split into volumes that are visible to the host systems that use them. See also “Capacity licensing” on page 782.
Virtualized storage
Virtualized storage is physical storage that has virtualization techniques applied to it by a virtualization engine.
Virtual local area network
Virtual local area network (VLAN) tagging separates network traffic at the layer 2 level for Ethernet transport. The system supports VLAN configuration on both IPv4 and IPv6 connections.
Virtual storage area network
A virtual storage area network (VSAN) is a logical fabric entity defined within the SAN. It can be defined on a single physical SAN switch or across multiple physical switched or directors. In VMware terminology, the VSAN is defined as a logical layer of storage capacity built from physical disk drives attached directly into the ESXi hosts. This solution is not considered for the scope of our publication.
Vital product data
Vital product data (VPD or VDP) is information that uniquely defines system, hardware, software, and microcode elements of a processing system.
Volume
A volume is an SVC logical device that appears to host systems that are attached to the SAN as a SCSI disk. Each volume is associated with exactly one I/O Group. A volume has a preferred node within the I/O Group. Before SVC 6.1, this volume was known as a VDisk.
Volume copy
A volume copy is a physical copy of the data that is stored on a volume. Mirrored volumes have two copies. Non-mirrored volumes have one copy.
Volume protection
To prevent active volumes or host mappings from inadvertent deletion, the system supports a global setting that prevents these objects from being deleted if the system detects that they have recent I/O activity. When you delete a volume, the system checks to verify whether it is part of a host mapping, FlashCopy mapping, or remote-copy relationship. In these cases, the system fails to delete the volume, unless the -force parameter is specified. Using the -force parameter can lead to unintentional deletions of volumes that are still active. Active means that the system detected recent I/O activity to the volume from any host.
Write-through mode
Write-through mode is a process in which data is written to a storage device at the same time that the data is cached.
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