After booting a server that had been powered off for some time, the 4-disk
raid5 device was up and running in read-only mode with one disk missing.
After a, in hindsight, hasty decision, "mdadm --manage --add /dev/md0
/dev/sdd" was executed to re-add the missing device to the array.
At this time, all hell broke loose :) The first thing that happened was
that sdd was added as a spare instead of re-added as expected. The second
thing was that a different disk, sdb, was kicked from the array because of
read/sata-bus errors. The root disk also bailed and the system had to be
powercycled.
The real problem, from the start, was probably that sdb was bad all along,
but from some reason sdd was the device missing from the array after the
initial boot.
Trying to read data from sdb gives read errors and timeouts, but I was
able to do "mdadm --examine" after resetting the sata port.
The current state is that, out of 4 disks two are good (sde and sdf), one
is (in error) marked as a spare (sdd), and the fourth device is unusable
(sdb).
What is the correct method do change the spare disk back to a data disk
and try to restart the array with 3 out of 4 devices (sdd, sde and sdf)?
The device has never had a spare, so I think that sdd used to be "Active
device 0" before this happened?
Possibly relevant data from mdadm --examine on the four devices:
sdb State : clean
sdb Events : 333560
sdb Device Role : Active device 3
sdb Array State : .AAA ('A' == active, '.' == missing)
sdd State : clean
sdd Events : 333562
sdd Device Role : spare
sdd Array State : .AA. ('A' == active, '.' == missing)
sde State : clean
sde Events : 333562
sde Device Role : Active device 1
sde Array State : .AA. ('A' == active, '.' == missing)
sdf State : clean
sdf Events : 333562
sdf Device Role : Active device 2
sdf Array State : .AA. ('A' == active, '.' == missing)
If no one else has any better suggestions, my best guess would be to:
"mdadm --create /dev/md0 --level=5 --raid-devices=4 --assume-clean
/dev/sdd /dev/sde /dev/sdf missing" (the device was created with default
values, metadata 1.2, chunk size 512K, layout left-symmetric).
(Other crazy ideas involve editing the superblock of sdd and making it
device 0 and then trying to start the array after that).
Best regards,
Tomas
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
