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
The first thing to do is to start to preserve information. You'll need data from
Recreating an array
When an array is created, the data areas are not written to, *provided* the array is created in degraded mode; that is 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 : permute_array.pl