Re: Replacing a failed disk "in advance"

[Jan Kasprzak <kas@fi.muni.cz>]

	Hi Ladislav,

Ladislav Mate wrote:
: > I have a RAID-5 volume of 8 physical disks. One of these disks failed the SMART
: > self-test with an unreadable block error. Unfortunately I have discovered
: > that there is _another_ bad block on another disk. It is a different block,
: > so the RAID-5 volume as a whole is still working. But as a whole, the
: > RAID-5 volume has at least two unreadable sectors on two different disks.
: > 
: > What is the best way to replace these two failing disks one by one without
: > the loss of data? I cannot mdadm --fail one of them, because the
: > subsequent rebuild on a new disk would fail on reading the other bad block.
: > 
: > I would like to add the ninth drive to the RAID-5 volume, and put a replica
: > of one of the failing drives to it. Then remove the just-replicated drive,
: > and do the same with the other failing drive.
: When you take a look in mdadm man page and search for --replace you'll find what you are looking for.
: 
: --replace
:        Mark listed devices as requiring replacement.  As soon as a spare is available, it will be rebuilt  and  will  replace
:        the marked device.  This is similar to marking a device as faulty, but the device remains in service during the recov-
:        ery process to increase resilience against multiple failures.  When the replacement  process  finishes,  the  replaced
:        device will be marked as faulty.
: 
: --with This  can  follow a list of --replace devices.  The devices listed after --with will be preferentially used to replace
:        the devices listed after --replace.  These device must already be spare devices in the array.

	OK, this seems to be a way to go.

	Unfortunately, the system in question is too old,
and its mdadm does not know about the --replace option, according to
mdadm --manage --help. So I will look for a newer mdadm and hope the old
kernel of that system supports the mdadm --replace.

	Thanks!

-Yenya

-- 
| Jan "Yenya" Kasprzak   <kas at {fi.muni.cz - work | yenya.net - private}> |
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| http://www.fi.muni.cz/~kas/     Journal: http://www.fi.muni.cz/~kas/blog/ |
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