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For example, if I had either a Linux server running mdadm or Windows OS performing RAID at the software level, would data recovery be possible if the system crashed? Are there tools to access the array should this happen?

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Are there tools to access the array should this happen?

Sure, For linux just boot a standard livecd. For Windows you might need to setup a new install on separate disks if the crash resulted in an un-bootable OS somehow.

The software RAID formats used by Linux and Windows have been around for a long time. There are companies that claim to be able to recover data in some of the more unusual types of failures/corruption, that can't be handled internally.

What would happen if the underlying OS running software RAID crashed?

Depends on exactly what you mean by crashed.

  • If the OS simply had a kernel panic/BOSD, it is unlikely that you would lose the entire volume. Though your recently modified data might not have been actually saved to the disk yet.
  • If you are talking about some hardware failure of the storage controller, or a drive, then you could lose data.
  • There is always a extremely small possibility that there is some bug in the software RAID code, that could result in extreme corruption of the volume, but the software RAID code in both Windows and Linux have been around for more then a decade, and have seen extensive usage.

  • Of course there are also failures, that can happen based on the type of RAID used. In the case of a RAID0, a loss of a single member, or corruption of a single member of the set, could result in a loss of everything, RAID0 is strongly discouraged for a reason.

Various RAID levels have different levels of recoverability. Likewize some filesystems are better designed to be able to survive in the case of corruption (read about features like journals, and check out zfs).

In any case. Remember. RAID is not a backup. You should have a backup system in place. RAID gives you better drive performance and some fault tolerance, not a backup.

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Ah yes, I always assume RAID is backup when indeed it is not. That puts it all into perspective and knowing there are tools to recover and access arrays on a failed OS is relieving. Thank you! –  user970638 Jan 12 '13 at 3:25
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