When RAID arrays go bad
April 5, 2005 7:58 PM   Subscribe

The 2x250Gb RAID1 array on my desktop system (WinXP) started throwing up 'Delayed write failure' errors and forcing mirroring on reboot. I unplugged the HDs and reinstalled Windows, but suspect a hardware failure. What's the best way to run diagnostics while minimising the risk of corrupted data being mirrored across? Plug in each drive separately, detach the array, or re-mirror and hope for the best?
posted by holgate to Computers & Internet (1 answer total)
First, back up your system! Break the mirror and back up BOTH disks separately, in full. Then play around with one disk and then other to see which causes Windows XP to start throwing errors. Stress test both disks.

As a stopgap, I might suggest switching from write-back to write-thru caching. How this is done varies according to your hardware -- sometimes it's not even an option for desktop-oriented (as opposed to server-oriented) hardware.

With write-back caching, data is written to the cache immediately but to the disk later (either when cache memory needs to be recycled or when some transaction counter / timer expires.) This is the "delayed write" that your system is complaining about. In write-through caching data is written to both cache and disk immediately -- safer but slower.

Did I mention backing up your system? If the data is important enough to warrant mirroring, then you should already have been following a regular backup procedure.
posted by randomstriker at 12:40 AM on April 6, 2005

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