At 04:01 PM 12/2/2011 -0500, Stuart D. Gathman wrote: >Both MD and LVM support >DISCARD, and discarded blocks are not necessarily synced >between mirror legs. Googled it--seems like DISCARD (aka TRIM) is about telling SSDs that blocks are no longer in use so that the SSDs can optimally release tracking of the storage. I can see how this might result in random data appearing in the "discarded" region. I don't see how the 'mdadm' mirror check will cope with that result unless SSDs return zeros or some other constant value when TRIMed blocks are subsequently read. However this is a hard-drive scenario--no SSDs. It would seem that hard drives generally will either ignore TRIM operations or via drive flags inform the kernel to not attempt them. So this leaves me with two LVs where it's clear that LVM mirroring failed to maintain synchronization at some point in the last year or two. Also based on this thread http://www.issociate.de/board/post/507507/SSD_-_TRIM_command.html it would seem TRIM is very much a bleeding-edge feature. Unlikely it appears in the CentOS 5.7 kernel in use on the affected system. So I'm sticking with "turkey" as the appropriate characterization of LVM mirroring. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
