On Tue, May 31, 2016 at 8:48 PM, Brad Campbell
<lists2009@xxxxxxxxxxxxxxx> wrote:
> Much better to try and get the array running in a read-only state with all
> disks in place and clone the data from the array rather than the disks after
> they've been ddrescued. In the case of a running array, a read error on one
> of the array members will see the RAID attempt to get the data from
> elsewhere (a reconstruction), whereas a read from a disc cloned with
> ddrescue will happily just report what was a faulty sector as a big pile of
> zeros, and *poof* your data is gone.
My understanding is that mdraid will kick out a drive with an unrecoverable
hardware error on a single sector. (Is this incorrect?) How do you add
the drive back in and get the raid in a read-only mode that won't kick out
drives for failures, thus allowing you to fully recover data on a (say)
raid5 with bad sectors on every drive at different sectors offsets?
I'm asking hypothetically. I have my arrays scrubbed weekly to prevent
this kind of surprise, and I keep multiple backups of my most important and
irreplaceable data.
In the past, I had a mirror that kept kicking out one drive. I never lost
any data. Between a decent backup policy and luck, I never experienced two
drive failures at the same time. It's likely that the drive was timing out
on an unrecoverable read error, but the OS gave up first. This was before
I knew to fix that default (mis)tuning, as was discussed here recently.
Last fall, that drive totally failed, and since, I've been paying much more
attention to care-and-maintenance!
Thanks,
Eddie
P.S. Sorry for the double-response to those on the CC list... I forgot
to tell gmail to use plain text.
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