Nataraj wrote:
Does software raid 1 compare checksums or otherwise verify that the same
bits are coming from both disks during reads? What I'm interested in,
is whether bit errors that were somehow undetected by the hardware would
be detected by the raid 1 software.
Thanks,
Nataraj
I've been thinking about this as well.
Fact is that with CentOS-5 kernels (but not with CentOS-4, as this
functionality became available in kernel 2.6.17) you could (or rather
_should_ regularly)
echo check > /sys/block/mdX/md/sync_action
to check agreement between the two (or more) copies. When this finishes,
/sys/block/mdX/md/mismatch_cnt shows you the number of mismatches. You
can fix these with
echo repair > /sys/block/mdX/md/sync_action
This applies to at least RAID1 and RAID5.
At this point the question arises: how does the "repair job" know which
copy is the correct one? I have no answer to this question.
BTW, there is - even with current kernels - no speed gain in using RAID1
- see http://kernelnewbies.org/KernelProjects/Raid1ReadBalancing .
HTH a bit,
Kay
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