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Wednesday, August 9. 2006
Data Scrub with Linux RAID or Die
It is absolutely critical to use data scrubbing with Linux software RAID. If you fail to do so, when one of the drives fail and the new one is put in place to resync with, the chance of losing all data is very high. When Linux resyncs a RAID array, it steps through each and every block on the disk(s) it is syncing from. If there are any bad blocks on the 'good' drives data scrubbing hasn't found (or data scrubbing isn't being used), that drive will also be marked as unusable. This renders your array useless unless an array is in use that can recover from multiple drive failures at the same time, or you have quite a few days to spend on manual recovery.See this information on how to do data scrubbing with Linux RAID for another description and instructions on how to do this.
More information on Linux RAID issues and its risks can be found at the following URLs:
http://www.nber.org/sys-admin/linux-nas-raid.html (see the "Why do drive failures come in pairs?" section)
http://linas.org/linux/peeves.html (see the The IDE/fsck/RAID Tirade)
This is unlikely to be fixed (current efforts seem to be in EVMS, a horrifically complicated solution so complex they can't even answer their own FAQ items). The best bet seems to be to pray for ZFS to be completed for Linux soon, which completely rethinks the problem without adding yet another complicated layer and vastly simplifies storage management.
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When I first saw this comment in my queue I almost deleted it thinking it was spam, the link being from Anonymous and with no description. It's actually an informative site with some valid points on issues with RAID.
Here is a more friendly link if you want to check it out:
Battle Against Any Raid Five/Four/Free
http://www.baarf.com/
Here is a more friendly link if you want to check it out:
Battle Against Any Raid Five/Four/Free
http://www.baarf.com/
was told about this after meeting up with some friends at LRUG, so got to put this in place quickly.
really glad he mentioned it,
John.
really glad he mentioned it,
John.