RAID Recovery

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Revision as of 10:25, 13 July 2007 by DavidGreaves (Talk | contribs)

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When Things Go Wrong

There are two kinds of failure with RAID systems: failures that reduce the resilience and failures that prevent the raid device from operating.

Normally a single disk failure will degrade the raid device but it will continue operating (that is the point of RAID after all).

However there will come a point when enough component devices fail that the raid device stops working.

If this happens then first of all: don't panic. Seriously. Don't rush into anything; don't issue any commands that will write to the disks (like mdadm -C , fsck or even mount etc).

The first thing to do is to start to preserve information. You'll need data from /var/log/messages, dmesg etc.

Recreating an array

When an array is created, the data areas are not written to *provided* the array is created in degraded mode; ie with a 'missing' device.

So if you somehow screw up your array and can't remember how it was originally created, you can re-run the create command using various permutations until the data is readable.

This perl script is an un-tested prototype :

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