SnapDrive
This chapter provides an overview of SnapDrive, which provides storage virtualization of
IBM System Storage N series volumes and Snapshot backup and restore operations over iSCSI or Fibre Channel (FCP) transport protocols.
The following topics are covered:
 
 
30.1 Challenges
Today’s enterprise IT administrator is challenged to provision storage quickly to support applications for new business initiatives, all on a minimal budget. For most IT administrators, it does not stop at this point. They also must protect the application against data corruption, disasters, and attacks with the help of well-planned backup mechanisms. Even more importantly, the backup process must not disrupt the service or the performance of the service.
To address these issues, administrators maintain their own set of scripts that are executed periodically or manually to speed up and automate the tasks of storage provisioning and backing up. But this situation comes with an additional burden of maintaining the scripts.
For example, if the host operating system is updated to a newer version, the output of the command used in the script or command syntax might change, resulting in a complete rewrite of the scripts.
Therefore, IT and host administrators require a solution that enables them to do these tasks:
•Quickly provision storage and bring it online from the host.
•Adapt to different operating systems and other environmental changes without requiring maintenance of scripts.
•Take backups without any performance degradation to the application.
•Schedule and maintain their own backup policies, depending on the type of application.
•Modify space allocations without taking applications offline.
30.2 SnapDrive overview
SnapDrive software provides a host administrator efficient storage and data management, including the ability to implement quick backup and restore policies for application data.
An IBM System Storage N series storage system provides SnapDrive for Windows and SnapDrive for UNIX solutions to address the issues described in 30.1, “Challenges” on page 438. SnapDrive helps host administrators provision storage and manage it directly from the host. SnapDrive gives flexibility to application administrators by enabling them to define their backup policies and, more importantly, it allows administrators to resize storage on the fly without any disruption of application service.
Both versions of SnapDrive simplify storage and data management by using the host operating system and IBM System Storage N series technologies, hiding the complexity of steps that must be executed on both the storage system and the host system, and removing the dependency on the storage administrator.
Key SnapDrive functionality includes storage provisioning on the host, consistent data Snapshots, and rapid application data recovery from Snapshots. SnapDrive complements the native file system and volume manager technology, and integrates seamlessly with the clustering technology supported by the host operating system to provide high availability of the service to its users (Figure 30-1).
Figure 30-1 Typical SnapDrive deployment
SnapDrive provides a layer of abstraction between an application running on the host operating system and the underlying IBM System Storage N series storage systems. Applications that are running on a server with SnapDrive use virtual disks (or LUNs) on IBM System Storage N series storage systems as though they were locally connected drives or mount points. It allows applications that require locally attached storage, such as DB2, Oracle database, Microsoft Exchange, and Microsoft SQL, to use IBM System Storage N series technologies, including Snapshot, flexible volumes, cloning, and space management technologies.
30.2.1 Components of SnapDrive
SnapDrive includes all the necessary drivers and software to manage interfaces, protocols, storage, and Snapshots. Snapshots are nondisruptive to applications and functions on execution. Snapshot backups can also be mirrored across LAN or WAN links for centralized archiving and disaster recovery.
SnapManager solutions are designed to invisibly use SnapDrive to trigger backups, restores, and mirroring of specific data sets.
30.2.2 Benefits of SnapDrive
Most of today’s enterprises use business-critical applications, and their IT and storage management teams face a number of challenges such as these:
•Support new business initiatives with a minimal increase in operating budget.
•Protect data from corruption, disasters, and attacks.
•Back up data without any performance degradation, quickly and consistently, without any errors.
SnapDrive addresses these problems by providing simplified and intuitive storage management and data protection from a host/server perspective. Here we list some important benefits of SnapDrive:
•It allows host and application administrators to quickly create virtual disks within a dynamic pool of storage that can be reallocated, scaled, and enlarged in real time, even while systems are accessing data.
•It allows dynamic on-the-fly file system expansion; new disks are usable within seconds.
•Snapshots provide rapid backup and restore capability with minimal resource and capacity requirements.
•It allows mirroring, data replication, and clustering for high availability.
•It supports multipath technology for high performance.
•It enables connecting to existing Snapshots from the original host or a different host.
•Independent of the underlying storage access media and protocol. SnapDrive supports FCP, iSCSI, and Network File System (NFS) as the transport protocols (NFS supports only Snapshot management).
•It provides a patented, high-performance, and low-latency file system with industry-leading reliability.
•It includes robust yet easy-to-use data and storage management features and software.
•It has industry-leading availability, exceeding 99.99% availability on nonclustered systems.
•It provides robust data integrity features, such as advanced RAID functionality and built-in file system checksums, help protect against disk drive failures and disk errors.
30.3 SnapDrive integration with the host operating system
After being installed, SnapDrive can be used to create and manage virtual disks on IBM System Storage N series storage systems from the host operating system. For Windows-based hosts, these appear as basic disks to Windows Server 2003, Windows Server 2008, and their applications. The virtual disks that reside on the IBM System Storage N series storage system can be expanded, unlike Windows-native basic disks.
SnapDrive is also used to create, delete, and manage all aspects of the application Snapshot backups (Figure 30-2). It allows applications that require locally attached storage to use IBM System Storage N series functionality. It has been estimated that SnapDrive saves 100 steps in the creation of virtual disks.
Figure 30-2 SnapDrive
30.4 Snapshots using SnapDrive
A Snapshot is a frozen, read-only image of a traditional volume, a FlexVol, or an aggregate that captures the state of the file system at a point in time. You use SnapDrive to ensure that you create consistent Snapshots in the event that you need to restore a LUN from that copy.
30.4.1 Consistent Snapshots
Snapshot operations on a single LUN actually make a Snapshot of all the LUNs on the volume. Because a storage system volume can contain LUNs from multiple hosts, the only consistent Snapshots are those of LUNs connected to the host that created the SnapDrive Snapshot. In other words, within a Snapshot, a LUN is not consistent if it is connected to any host other than the one that initiated the Snapshot. (This is why you are advised to dedicate your storage system volumes to individual hosts.) Therefore, it is important to back up a LUN using a SnapDrive Snapshot rather than using other means, such as creating Snapshots from the storage system console.
Snapshots in SAN and NAS environments
Making Snapshots in a SAN environment differs from doing so in an NAS environment in one fundamental way: In a SAN environment, the storage system does not control the state of the file system.
Snapshots are useful only when they can be successfully restored. Snapshots of a single storage system volume that contains all the LUNs on the host file system are always consistent, provided that the file system supports the freeze operation. But if the LUNs on the host file system span different storage system volumes or storage systems, then the copies might not be consistent, unless they are made at exactly the same time across different storage system volumes or storage systems and they can be restored successfully. For UNIX, consistent Snapshots can be created using the Data ONTAP consistency group feature, which is supported beginning with Data ONTAP V7.2.
SnapDrive and SnapManager for Oracle
One of the major deployments for SnapDrive is deploying along with SnapManager for Oracle. SnapManager for Oracle has become one of the most popular tools for making and managing backups for Oracle in an IBM System Storage N series environment. SnapManager for Oracle relies on SnapDrive to execute all backup and restore commands on the storage system.
For more information about the SnapManager for Oracle product, see the following website:
 
Attention: If you use the SnapManager product to manage your database instead of SnapDrive, you must use SnapManager to create Snapshots.
30.4.2 Preferred practices for Snapshots
For space management when using SnapDrive, use the following preferred practices:
•Disable automatic Snapshot creation on the storage system for the volume on which the LUNs are created.
•Periodically, use the snapdrive snap list command and delete old Snapshots that can unnecessarily occupy space.
•Set the snap reserve value to 0%, because the automatic Snapshots that are made by the storage system might not capture the LUN in a consistent state and therefore allow use of all the volume space dedicated for the LUNs.
•Use SnapDrive to create and manage all the LUNs on your storage system.
•Place all LUNs connected to the same host on a dedicated volume accessible by just that host.
•To avoid space contentions, do not have LUNs on the same storage system volume as other data (for example, NFS share).
•Unless you can be sure that name resolution publishes only the storage system interface that you intend, configure each network interface by IP address, rather than by name.
•If you use Snapshots, you cannot use the entire space on a storage system volume to store your LUN. The storage system volume hosting the LUN must also include sufficient space to store the Snapshot delta (incremental changes over time). This overhead can vary significantly depending on the volume settings, Snapshot retention schedule, and rate of change, and needs to be carefully planned.
•Do not create any LUNs in /vol/vol0. It is a storage system limitation. This volume is used by Data ONTAP to administer the storage system and must not be used to contain any LUNs.
30.4.3 Volume-size rules
SnapDrive uses space on a storage system volume for LUNs and their data, and also for the data that changes between Snapshots, the LUN's active file system, and for metadata.
Storage system volumes that will hold LUNs must be large enough to hold all the LUNs in the volume, as well any Snapshots if Snapshots are created.
The following factors govern the appropriate minimum size for a volume that holds a LUN:
•The volume and LUN settings must be configured as per the N series preferred practices. For example: Fractional Reserve, Volume Autosize, Snapshot Autodelete, and LUN and/or volume thin provisioning. The specific combination of settings will vary depending on your environment and intention.
•The volume must be at least as large as the LUN that it is to contain.
•The volume must also provide enough additional space to hold the number of Snapshots that you intend to keep online.
The amount of space consumed by a Snapshot depends on the amount of data that changes after the Snapshot is taken. The maximum number of Snapshots is 255 per storage system volume.
•If you are not implementing the automatic capacity and Snapshot management features (that is, not following preferred practice) then we advise that you set the volume size to be twice the LUN size, plus some additional overhead to store the Snapshot delta (such as 20%).
 
Tip: Although this configuration is common in legacy systems, we advise that you instead use the modern preferred practices, as they significantly reduce capacity overhead.
30.5 SnapDrive for Windows
SnapDrive enables Windows and UNIX applications to access storage resources on IBM System Storage N series storage systems, which are presented to the Windows 2003 (or later) operating system as locally attached disks. IBM System Storage N series storage systems and SnapDrive software represent a complete data management solution for Windows applications.
SnapDrive includes Windows 2003 and later device drivers and software that is used to manage application Snapshot backups. Snapshot backups, shown in Figure 30-3, are nondisruptive to applications and occur quickly. Restoring data from a Snapshot is nearly instantaneous. Snapshot backups can also be mirrored across LAN or WAN links for centralized archiving and disaster recovery purposes. This section provides a brief outline of the architecture of SnapDrive.
Figure 30-3 Snapshot
30.5.1 SnapDrive software components
SnapDrive software combines IBM System Storage N series functionality, Windows 2003 and later IBM System Storage N series device drivers, and a Microsoft Management Console (MMC) application into a complete data management solution.
The SnapDrive software installed on a Windows 2003 server has the following components:
•SnapDrive Win32 device drivers
•SnapDrive Win32 service
•SnapDrive Microsoft Management Console application
30.5.2 Windows Device Manager
In the SCSI and RAID controllers section of the Windows Device Manager, the Emulex LightPulse PCI Fibre Channel HBA and Microsoft iSCSI Initiator are both visible, as shown in Figure 30-4. SnapDrive is capable of accessing virtual disks over iSCSI and FCP on one or more storage systems simultaneously.
Figure 30-4 Computer management
Figure 30-5 shows the SnapDrive MMC management interface, which is used to manage virtual disks. In this example, there are two LUNs in use by this server.
Figure 30-5 SnapDrive
After it is installed, SnapDrive can be used to create and manage virtual disks on IBM System Storage N series storage systems, which appear as basic disks to the Windows 2003 server and its applications. Virtual disks that reside on an IBM System Storage N series storage system can be expanded, unlike Windows-native basic disks. SnapDrive is also used to create, delete, and manage all aspects of the application Snapshot backups.
After a SnapDrive virtual disk is created, it appears in the Microsoft Disk manager, as shown in Figure 30-6.
Figure 30-6 Microsoft Disk Manager
30.5.3 Dynamic file system expansion
As your storage needs increase, you might need to expand a virtual disk to hold more data.
A good opportunity for doing this task is right after you have expanded your IBM System Storage N series volumes.
Planned downtime is also minimized with online disk expansion. Scheduled maintenance is minimized. Dynamic file system expansion satisfies those unique occurrences when unplanned growth or data movement is required and capacity must be increased on the fly. The following figures show how easily It can be done.
Figure 30-7 shows disk expansion.
Figure 30-7 Disk expansion
Figure 30-8 shows dynamic expansion.
Figure 30-8 Dynamic expansion
30.5.4 Volumes, RAID groups, and virtual disks
Physical disks are grouped together in the form of volumes on an IBM System Storage N series storage system and can consist of one or more RAID groups.
Virtual disks are created and managed within the limits of an IBM System Storage N series storage system available storage capacity on a per-volume basis. The size of a volume is determined by the number of disks multiplied by the capacity of the disks.
The disks that make up a single volume can be divided into multiple RAID groups. Each RAID group calculates parity information for the drives within the RAID group. The use of multiple RAID groups is transparent to data access and only important at the RAID layer. Volumes function as a whole regardless of the number of RAID groups.
Application programs that run on a Windows server (such as a database application) access virtual disks as though they were locally attached physical disks. Virtual disks are units of storage that are designated for use by one or more host servers.
Virtual disks can also be used with Microsoft Cluster Server (MSCS). MSCS can use virtual disks for data storage and as quorum disks. Virtual disks and their attributes (such as file system format (NTFS) and size) are defined by the system administrator.
Consider the following points regarding virtual disks:
•Virtual disks are created on the IBM System Storage N series storage system and mounted as disks on Windows servers.
•Virtual disks are accessed and function as physical disks to the Windows server.
•Virtual disks appear within Windows as basic disks, not dynamic disks.
•Virtual disks can be expanded, unlike the native basic disks within Windows.
•Virtual disks are formatted with the NTFS file system.
•Virtual disks reside on physical N series volumes that are RAID protected and distributed among multiple disks for maximum data integrity and performance. See Figure 30-9.
Figure 30-9 RAID-DP
•Dynamic-disk features and functionality are provided by the IBM System Storage N series storage system.
•Multiple virtual disks can be created on a single IBM System Storage N series storage system volume.
•Virtual disks can be accessed using the iSCSI over Gigabit Ethernet or FCP over Fibre Channel access methods.
30.6 SnapDrive for UNIX
SnapDrive for UNIX is a tool that simplifies the backup of data so that you can recover it if it is accidentally deleted or modified. SnapDrive for UNIX uses IBM System Storage N series Snapshot technology to create an image (that is, a Snapshot) of the data on a storage system attached to a UNIX host at a specific point in time. If the need arises later, you can restore the data to the storage system. When you restore a Snapshot, it replaces the current data on the storage system with the image of the data in the Snapshot.
In addition, SnapDrive for UNIX lets you provision storage on the storage system. SnapDrive for UNIX provides a number of storage features that enable you to manage the entire storage hierarchy, from the host-side application-visible file through the volume manager to the storage system-side LUNs providing the actual repository.
SnapDrive for UNIX is supported on the following host platforms:
•IBM AIX
•HP-UX
•Linux: Includes Red Hat Enterprise Linux, SUSE Linux, and Oracle Enterprise Linux.
•Solaris
SnapDrive for UNIX has the following key features:
•Advanced storage virtualization: Virtualizes IBM System Storage N series storage systems and integrates with native disk and volume management
•Automated mapping and management of new storage resources: Provisions new storage resources cleanly and efficiently, without application or server downtime
•Dynamic storage allocation: Quickly and easily reallocates storage systems in response to shifts in application or server demand
•Host file system consistent Snapshots: Implements a mechanism by which Snapshots taken are file system consistent
•Backup and restore: Provides a quicker way to create and restore storage from backups using IBM System Storage N series Snapshot technology
SnapDrive for UNIX allows you to create and delete a storage LUN or connect to a LUN that has already been created on the storage controller. If you must perform these tasks without SnapDrive for UNIX, you must log in to the storage system to create and map a LUN. Then, from the host and using the host commands, identify the LUN on the host, create a file system, and mount it. SnapDrive for UNIX achieves all these tasks with one command, reducing the time and probable errors during this process (Figure 30-11).
Although SnapDrive for UNIX can create storage using minimal options, you still need to understand the default values and use them appropriately.
 
Attention: SnapDrive for UNIX works only with Snapshots that it creates. It cannot restore Snapshots that it did not create.
30.6.1 How SnapDrive for UNIX works
The SnapDrive for UNIX software interacts with the host operating system and volume manager. It lets you easily and quickly back up and restore data about host volume groups that you stored on an IBM System Storage N series storage system. You can use it to manage the Snapshots that you create using it.
SnapDrive for UNIX coordinates the host Logical Volume Manager (LVM) volume groups and file systems to ensure that the host file systems stored on IBM System Storage N series LUNs have consistent images in the Snapshot. This action enables you to restore data from the backup Snapshots without requiring significant data recovery steps on the host.
You can also use SnapDrive for UNIX to create and manage storage. The SnapDrive storage commands, shown in Figure 30-10, work with LVM to let you create LVM objects and file systems that use the storage. They also let you remove the mappings between the storage and the host and delete the storage.
Figure 30-10 UNIX SnapDrive
SnapDrive for UNIX communicates with the storage system using the host IP interface that you specified when you set up the storage system.
30.6.2 SnapDrive for UNIX and logical volumes
The host LVM combines LUNs from a storage system into disk or volume groups. This storage is then divided into logical volumes, which are used as though they were raw disk devices to hold file systems or raw data.
 
Volumes: This book refers to logical volumes as host volumes to distinguish them from IBM System Storage N series storage system volumes.
SnapDrive for UNIX integrates with the host LVM to determine which IBM System Storage N series LUNs, as shown in Figure 30-11, make up each disk group, host volume, and file system requested for Snapshot. Because data from any given host volume can be distributed across all disks in the disk group, Snapshots can be taken and restored only for entire disk groups.
Figure 30-11 IBM System Storage N series LUNS
30.7 Flexible networked storage
SnapDrive is independent of the underlying storage access media and protocol. The iSCSI protocol provides storage access when the IBM System Storage N series storage system and host server are joined using Gigabit Ethernet. The FCP protocol facilitates storage access through a Fibre Channel host bus adapter (HBA) and storage area network (SAN).
The functionality and features intrinsic to SnapDrive are identical regardless of the underlying storage access protocol. It is because SnapDrive software utilizes either of the two access methods to access virtual disks, which are created and stored on storage systems. Thus, a virtual disk can be created and accessed using the iSCSI or FCP access protocols.
Virtual disks are referred to as logical unit numbers (LUNs) when accessed over the iSCSI and FCP protocols. Within the IBM System Storage N series storage system, LUNs are just special files.
30.8 Summary
SnapDrive is a complete storage management solution. It helps administrators execute nearly instantaneous Snapshot backups and restorations of application data. It also provisions storage from the host system as required by each application.
 
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