RAID Rant: RAID is NOT Backup!

Data Backup Storage Information TileWith the loss of  Drive Extender in WHS and my search through RAID alternatives I’ve noticed a lot of people equate RAID (and RAID like solutions) with backup. RAID is not backup. RAID provides redundancy for one hardware component to improve uptime (and RAID 0 doesn’t even provide that).

So let’s get RAID 0 out of the way. This is also called “scary RAID” for good reason. With RAID 0 data is “stripped” across multiple physical drives so that there’s one big drive. This is usually done to improve performance but if any one drive fails then any data is lost. So clearly no way anyone would consider this “backup”.

Then there’s RAID 1 (Mirroring) where the files are written to two drives which are a mirror of each other. Two physical file copies, so that’s backup, right?  A see a lot of mentions that this provides two copies of the files. Nope. If one drive fails the other drive can keep the system running or feeding data, but what if:

  • You delete a file? – the deletion is mirrored across both drives.
  • A file is corrupted? – The corruption is written to both drives.
  • The controller/motherboard fails? – The drives are inaccessible until the broken part is replaced. If the controller failure didn’t corrupt the drives and you replace the hardware with like hardware (or correctly reconfigure the software RAID) you’ll probably be able to get the system back. Depending on the OS and RAID implementation you might be able to take one of those drives and attach it to another computer to get at the files. Assuming the failure didn’t corrupt the files.
  • A virus deletes your files? – the deletions are mirrored.
  • A power surge zaps your PC? – It’s as likely to fry two drives as it is one.
  • You screw things up when upgrading/reconfiguring your PC? – Oops
  • A water pipe breaks and floods your computer case? (or someone spills a drink into it)? – oh well
  • And so on…

RAID 5 provides redundancy through a check-bit rather than keeping a mirror but the potential problems are the same. There are still the same issues and if two drives are lost then it’s all lost. (There are more involved RAID solutions that can support multiple drive failures, but that’s the only additional protection they provide.)

In the case of Windows Home Server Version 1 the folder duplication feature has the same limitations of RAID 1. Redundancy, not backup. I kept all my WHS v1 files duplicated because it would have been a huge pain to lose one non-duplicated drive in the pool and cause a lot of down time. So I duplicated it all – and still did backups.

With WHS v2 I’ve become less fanatical about uptime. I have a RAID 5 array for the files that are critical and for when I need more than 2 TB of space in one share. But my video files (the bulk of my data is video) is spread across individual drives. The RAID array provides improved reliability for the files I really need and might not want to wait on a restore or rebuild. Since these are my most critical files they are backed up multiple times (some have 3 backups while the rest have 2 – in addition to the files on the RAID array). I have more backups of these than my video files that aren’t RAID protected.

There’s nothing wrong with RAID, just don’t confuse it with a backup.

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