On Thu, Dec 10, 2009 at 6:00 PM, Marco Peereboom <slash@peereboom.us> wrote:
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>> Does this mean there's little advantage of hardware mirror raid over
software?
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>> So software mirror raid increases chances of data corruption while
decreasing
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>> the chances of downtime. True for hardware as well?
>
> There are pro and cons to both solutions.  Pick what makes sense in your
> scenario.
>
>> Hmmm. I've used hardware raid cards for mirrors that have the verify
function.
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>> It would be interesting to know how and what those cards do.
>
> They read the data to make sure the disk is working.  If one disk is
> failed they can rebuild that block from the remaining disk provided that
> the remaining disk isn't corrupt or broken too.  They assume that the
> data that was read is accurate; if it isn't you are SOL.
>
> They either don't detect or ignore blocks that are different because
> they can not know which one is accurate (if any).
>
> Verify for RAID 1 is mostly marketing fluff.

Thanks a lot for this info. In the past I've had weird corruption of
files with a
raid card - some files on the volume would become corrupt, but the
corruption was limited
to files only. IOW the whole volume would be intact and I could write
and read new files to it
but as the time went some individual files would contain garbage
instead of real data. I wonder
what that was all about.