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Ext3 and write caching by drives are the data killers...Ext3 and write caching by drives are the data killers...Posted Sep 1, 2009 23:49 UTC (Tue) by dododge (subscriber, #2870)In reply to: Ext3 and write caching by drives are the data killers... by Cato Parent article: Ext3 and RAID: silent data killers?
Well for starters (unless things have changed recently) LVM doesn't support write barriers, so if you put LVM in the loop it probably doesn't matter if the drive reports write completion correctly or not. If you use XFS on top of LVM you get a big warning about this at mount time.
I don't use EXT3 much, but from a quick googling it sounds like you have to explicitly turn on barrier support in fstab and it still won't warn you about the LVM issue until it actually tries to use one.
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Ext3 and write caching by drives are the data killers... Posted Sep 2, 2009 7:18 UTC (Wed) by Cato (subscriber, #7643) [Link]
You are right on both points - when ext3 tries to do barriers on top of LVM it complains at that point, not at time of mounting.
Ext3 and write caching by drives are the data killers... Posted Sep 3, 2009 7:18 UTC (Thu) by job (guest, #670) [Link]
According to previous comments at LWN barriers should be working through LVM with 2.6.30.
LVM barriers Posted Sep 3, 2009 10:23 UTC (Thu) by Cato (subscriber, #7643) [Link]
There are some limitations on this - LVM barriers will only work with a linear target, apparently: http://lwn.net/Articles/326597/
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