Raid
and server faults: Avoiding data loss
How
the data is stored: Typically the data you wish to recover
will be written across all the disks that make up the RAID array.
From a data recovery angle, this typically means that complete
individual files will not exist on any one disk,
but rather segments of each file will be distributed across the
whole RAID array. It's therefore pointless (unless you are trying
to recover data from a mirrored raid [RAID 1]) to attempt to isolate
a single drive from the array and recover that.
Golden rules of RAID data recovery:
DO
NOT change the disk order of the array: It's very
important not to change the order of the disks in the RAID array.
Infact, unless you have a physical problem with one or more disks
in the array, you shouldn't need to remove them from the server.
If you do remove them, it is vitally important that you
put them back in the same order. Under no circumstances
should you attempt to recover the data from a RAID array if the
drive order has been compromised. You run an extremely
high risk of losing all the data.
DO
NOT run disk checking software on the array: Scandisk
and Chkdsk are programs that often run automatically if a problem
with the filesystem is detected. Unfortunately, these
programs are unable to deal with physical damage to hard disks,
and even more unfortunately, rather than terminate, they will
carry on and attempt to fix any problems. For further information,
please read our page detailing why it's not a good idea to run
scandisk
/ chkdsk on raid arrays.
DO NOT continue to
run the system if one or more of the hard disks appear faulty:
If the RAID / SCSI BIOS reports that one or more drives are not
functioning correctly, you may have a physical
drive problem. Sometimes however, the BIOS
will indicate that drives are offline not because of a physical
disk problem, but rather because of a RAID configuration problem.
DO NOT re- configure
the RAID: If there does not appear to be a problem
with the RAID configuration, there is no need to write any new
configuration data. If the configuration information has been
lost or corrupted it's imperative that the RAID is re-configured
correctly.
The most important Golden Rule:
DO NOT rebuild the
RAID: If any of the points above apply or you
are uncertain about the viability of your data, DO NOT
REBUILD THE RAID.
> Back to the MAIN data
recovery page
