Why You Might Care About a Striped RAID, JBOD, or Concatenated Storage

The highest-capacity individual drive mechanism available to the general public in early 2019 holds 14 TB. (At publication time, prices start around $500.) But you might have more than 14 TB of data to back up, or be unable to afford a single jumbo-sized drive. There’s a solution: a number of companies sell devices that appear to be external hard drives but hold more than 14 TB, because their cases contain multiple drive mechanisms (for example, two 8 TB disks). The enclosure’s circuitry combines the two disks into a larger volume; sometimes it’s a high-performance striped RAID 0 volume, sometimes it’s merely concatenated, and sometimes it’s JBOD but with hardware or software features that let you reconfigure it as a RAID (perhaps even a mirrored RAID 1, for more fault tolerance but half the capacity).

The good news is that such devices offer the benefit of a large, fast disk without making you cobble together your own hardware- or software-based RAID and deal with lots of boxes and cables. The bad news is that if you use RAID 0 and a mechanism in your enclosure dies, you could lose all the data on both drives. Even in the best case, you’ll have to send the device back to the manufacturer for repair. And, if one of two or more concatenated disks fails, you may not be able to get the data on the remaining disk(s) without the manufacturer’s intervention.

I’m not saying you should avoid such devices; I’m saying you should know what you’re getting into if you rely on them. Mathematically, your chances of losing the data on RAID 0 or concatenated disks are at least double that of a single mechanism of the same type. So if you get a multi-drive enclosure and have the choice, I suggest that you use RAID 1 or higher, because all levels of RAID beyond 0 offer redundancy to protect data in case of drive failure (along with a reduction in capacity).

Why You Might Care About a Mirrored RAID

Mirrored RAIDs have at least two copies of your data, so, unlike striped RAIDs, they protect you against drive failure. The downside is that you need twice as many disks for a given amount of capacity. Some people believe that a mirrored RAID consisting of their Mac’s internal drive plus an external drive of the same capacity is effectively the same thing as a duplicate—only better, because it’s always 100% up to date. I beg to differ.

I have nothing against mirrored RAIDs. However, a RAID, by itself, is no substitute for multiple duplicates as described in this book. A mirrored RAID’s best feature is also its Achilles’ heel: because changes are reflected on all drives at once, an accidentally deleted (or damaged) file will be immediately deleted (or damaged) on your “backup” drives too! (Standalone duplicates—especially if you maintain two or more of them—reduce this risk greatly.) RAIDs address the problem of drive failures but provide no insurance against human error, theft, or any of the other catastrophes that make backups so important. And, like backups stored on extra internal hard drives, RAIDs do you no good if your computer is stolen or in the shop for repairs.

So, if you use a mirrored RAID to protect yourself against drive failure, that’s fine…but you still need a separate bootable duplicate. (A mirrored RAID with more than two disks can, in certain situations, substitute for a bootable duplicate; I explain one way to set this up ahead, in Creating a RAID with SoftRAID.)

The BeyondRAID system used in Drobo devices also provides data redundancy, and can also (in some cases) be used as a bootable duplicate. However, Drobo’s benefits and limitations are fundamentally different from those of a conventional mirrored RAID, as I explain in Drobo Storage Devices.

Creating a RAID with SoftRAID

I said earlier that you can join multiple external disks into a RAID using either software or a special hardware controller. Apple’s Disk Utility lets you create simple software RAIDs. (This capability disappeared in 10.11 El Capitan but was restored in 10.12 Sierra.) For anyone needing more flexibility than what Disk Utility offers (or for Mac users running El Capitan), the best tool for the job is SoftRAID. Install this software (included free with some multi-drive enclosures) and you can create a RAID with any of several configurations and modify it as necessary if you add or replace hard drives.

For the purpose of this book, what I find most interesting about SoftRAID is that when it comes to bootable duplicates, it lets you have your cake and eat it too. You can create a RAID in which your internal disk is mirrored onto two or more external drives at once. Then, periodically rotate one of the drives offsite, where it will function as a standalone duplicate of your disk at an earlier state. When you plug it back into your Mac, it will automatically synchronize with the remaining drives in the RAID. The beauty of this approach is that you never have to set up, schedule, or run backup software to make duplicates; it happens automatically and is always perfectly up to date.

You’ll still need a separate way to handle versioned backups, of course, such as Time Machine or ChronoSync. One extremely clever configuration is to split each of your external drives into two partitions—one for your mirror and one for your versioned backups. That way, you don’t have to maintain separate drives for each purpose—whichever drive you have connected at any moment will be both a mirror (and, when disconnected, a bootable duplicate) and a versioned backup.

To pull this off, you’ll need the full version of SoftRAID and two or more external drives, each with plenty of capacity (ideally, three or more times that of your internal drive). For example, if I were doing this on a Mac with a 1 TB SSD, I’d use 4 TB external drives. I refer you to the SoftRAID documentation for the details of each step, but the broad outline is as follows:

1. With SoftRAID installed on your Mac, create a bootable duplicate of your startup volume (see Create and Use a Bootable Duplicate).

2. Boot your Mac from the duplicate.

3. Connect the (blank) external drive you’ll use for the RAID.

4. Use SoftRAID to initialize your Mac’s internal disk and the external disk.

5. Create a mirror (RAID 1) volume with these two disks.

6. Still using SoftRAID, create a second volume with the remaining partition space on the external drive. This is what you’ll use for your versioned backups.

7. Use whichever app you employed in step 1 to clone your current startup volume (the bootable duplicate) back onto the new RAID.

8. Open SoftRAID again, select the newly cloned volume, and choose Volume > Rebuild Boot Cache. (Without this step, your Mac won’t boot from the RAID.)

9. Go to System Preferences > Startup Disk, select the newly created RAID as your startup disk, and click Restart.

Once your Mac has restarted from the RAID, you can set up Time Machine (or another backup app) to store versioned backups on the external drive’s spare partition. Then, if you want to include another external drive in the RAID, you can connect it and use SoftRAID to initialize it and add it to your existing RAID volume.

Whenever you disconnect an external drive from your RAID, your Mac continues running from the internal drive (and the remaining external drives, if any), but if you disconnect all the external drives, Time Machine won’t run until one of them is reconnected. Reconnecting a drive that’s part of the RAID causes it to rebuild itself automatically, so that it matches the internal drive.

This configuration amounts to a nearly bulletproof backup system. As long as you remember to swap external drives periodically (say, once a day), you’ll have all the benefits of a mirrored RAID, a bootable duplicate, and a versioned backup. Great, right? (Granted, this solution works better for desktop Macs than for laptops, because it requires you to keep at least one external drive attached much of the time.)

There are, however, some limitations in SoftRAID 5.7.3 (the latest version shipping at publication time) and earlier that you’ll want to be aware of:

• SoftRAID 5.x doesn’t support APFS drives at all, so if you’re running High Sierra or Mojave and your startup disk is formatted as APFS, SoftRAID would be useful only for other, non-startup volumes.

• SoftRAID does not support any disk configuration that depends on Apple’s CoreStorage technology, which includes both Fusion drives and FileVault when the drive is formatted using the HFS Plus file system. (Again, SoftRAID 6 running on APFS drives should fix this.)

• If you’re using one or more hard drives in a mirrored RAID along with an SSD startup volume, your overall performance could suffer since the hard drives will be unable to read and write data as quickly as the SSD. Of course, you can add external SSDs to a RAID…if you can afford them!

I can’t wait for version 6.0 to appear, because a multi-drive, bootable, encrypted, mirrored RAID setup with versioned backups as I’ve described here has been a goal of mine for a number of years!

Drobo Storage Devices

Drobo storage devices are much like RAIDs, in that they let you combine multiple disks into a single, higher-capacity volume. Depending on the model, a Drobo can hold anywhere from five to eight hard drive (or SSD) mechanisms. Some have local interfaces such as USB 3.0, Thunderbolt 2, or Thunderbolt 3; others have gigabit Ethernet interfaces. Although the models have various other differences too, they all have the following in common:

• You can hot-swap drives.

• You can mix and match drives—any number, capacity, speed, or manufacturer.

• Part of the space on each drive is set aside for data redundancy, so if any single drive fails, all the data remains intact. You can simply swap out the malfunctioning drive as if nothing happened.

• The Drobo automatically reconfigures itself as you add or remove drives; no manual intervention is required at all.

This set of capabilities (along with a few other niceties) is collectively known as BeyondRAID. That’s an apt name, because Drobo does all the things a RAID can do and then some. With a conventional RAID, for example, all disks must have the same capacity, and adding or removing a volume requires lengthy, tedious reconfiguration.

As a result, a Drobo is a good way to ensure you always have enough capacity for your backups. All Drobo models work with Time Machine, and those with local interfaces can also be used as Mac boot volumes. You can even partition a Drobo into two volumes, one for bootable duplicates and the other for versioned backups.

However, even though you can use a Drobo for bootable duplicates and can remove one (or in some cases two) of them without data loss, you cannot boot from any individual drive, nor can you use the drives apart from the entire set to reconstruct your disk. That means the trick I described earlier with SoftRAID—using two or more mirrored disks and rotating one offsite in lieu of maintaining separate bootable duplicates—isn’t feasible with a Drobo. And although you could back up to two or more Drobos and rotate one offsite, the hassle and expense of doing so may be prohibitive.

So, while it could be a valuable component of a backup system, especially if you work with extremely large files, a Drobo alone probably won’t meet all your backup needs.

Network Storage Devices

The term NAS, or network-attached storage, typically refers to a box containing one or more hard drives, a bit of computing power, and a wired or wireless network interface—sort of a minimalist file server. (Sometimes NAS devices are simply called network drives.)

Ethernet-equipped Drobo models are examples of NAS devices. Apple’s Time Capsule was also a type of NAS device (more on this in a moment). Similarly, an Apple AirPort Extreme Base Station with an external USB drive (an AirPort Disk) could be considered a NAS, but only the most recent (tower-shaped) AirPort Extreme models let you use an AirPort Disk for Time Machine backups.

NAS devices are frequently marketed as backup (and all-purpose file storage) solutions for small networks. The idea is that you can set up a centralized file server without needing an additional computer, and every computer on your network can back up files to it. Some NAS equipment can also communicate with your home entertainment system, providing storage for audio and video. And newer NAS devices that use the Btrfs file system can take snapshots of your data manually or at scheduled intervals, which produces an effect similar to storing versioned backups: you can at any time restore your data to its state when a snapshot was taken.

Although a NAS device can indeed be useful in many situations, you should keep in mind a few important considerations when thinking about using one as a backup destination:

• Some NAS models can run their own backup software (that is, the NAS runs the server app, and each of your Macs runs a client). That’s a perfectly valid setup, but because you can’t install just any arbitrary backup software on any given NAS, you may be stuck with whatever app the manufacturer offers, or whatever third-party options may be available for that particular platform. This approach may limit your flexibility and prevent you from setting up your backups in precisely the way you’d prefer.

• If your NAS can’t run its own backup software—or if you’re unhappy with the software it offers—you can still use it for push backups (see Network Backup Approaches) and run the backup app of your choice on each Mac. Performance and reliability may take a hit over what client-server backups offer, however.

• Irrespective of the points above, some NAS models—mostly newer ones—support Time Machine. If the model you choose does, you can follow the manufacturer’s instructions to set it up as a destination for your Macs. But be sure to confirm compatibility before you make your purchase.

• Some older NAS devices can only be formatted using FAT32, a Windows file system. Although macOS can read from and write to FAT32 volumes, some metadata may not be stored properly. Your backup software may address this limitation by storing data in a special archive file, but if it backs up files in a Finder-readable format, you risk losing data.

• You can’t create a bootable duplicate onto a NAS (and even if you could, you wouldn’t be able to boot your Mac from it). The only way to create a bootable duplicate over a network is to back up to a drive connected to a Mac running one of a very few backup apps specially designed for this purpose (Carbon Copy Cloner, ChronoSync, or Retrospect).

• And don’t forget, your NAS itself should be backed up to another destination; see Back Up a NAS.

All that said, with the right hardware and software a NAS can make an excellent storage medium for versioned backups of several computers’ files, and thus a valuable component of a broader backup strategy.

For those wanting to use Time Machine to back up to a NAS, Apple’s AirPort Time Capsule was once the optimal solution. Even though it was more expensive than competing products, it was expressly designed to work in this configuration. Unfortunately, as I mentioned in Time Capsules Officially Bite the Dust, since the previous version of this book was published Apple stopped selling the Time Capsule and all other AirPort products. If you still have one, you can use it (until the hardware eventually fails), but it’s no longer a good long-term solution.

Local Network Servers

If, in your home or office, a Mac or PC is functioning as a file server, it’s worth considering whether you could use a network volume as a backup destination. After all, a full-blown computer is likely to give you both better performance and greater flexibility than even the fanciest NAS. (And, if you have the computer already, you won’t need to buy another device.)

In general, if you have control over the server yourself and it’s not already bogged down with other tasks, using it for backups is a fine idea. I strongly recommend adding a separate physical hard drive, and either configuring the server—if it’s a Mac running High Sierra or later—as a Time Machine server (see Use a Mac as a Time Machine Server) or installing client-server backup software (see Network Backup Approaches). Otherwise, your backups will be commingled with other files, making it difficult to store them offsite and potentially creating a security risk.

If you do not personally have control over the server (for example, if it’s a shared company server), resist the urge to use it for backups. You could easily use up more space and network bandwidth than you should (thus incurring the wrath of your IT department), and you’ll have less control over your data than if you use local media.