raid6: Disk failure on sdb1, disabling device.

[jippie]

For backup purposes, I built a RAID6 array on USB. When during the night the backup filesystem is being mounted, every so many days, a random disk fails:

sd 9:0:0:0: [sdb] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
sd 9:0:0:0: [sdb] Sense Key : Illegal Request [current]
sd 9:0:0:0: [sdb] Add. Sense: Invalid field in cdb
end_request: I/O error, dev sdb, sector 2930271935
end_request: I/O error, dev sdb, sector 2930271935
md: super_written gets error=-5, uptodate=0
raid5: Disk failure on sdb1, disabling device.
raid5: Operation continuing on 3 devices.

To fix my RAID set I do the following:

mdadm /dev/md2 --fail /dev/sdb1
mdadm /dev/md2 --remove /dev/sdb1
mdadm /dev/md2 --add /dev/sdb1

And it starts to sync for many many hours...

In other words, my RAID set fails every so many mounts, but I know how to fix it.
What I want to find out is:
- Why is a random drive failed every now and then?
- How can I prevent that drive from being failed?


BTW: I have a second RAID set that has been functioning for years without error, so the setup I use must be correct. The only difference between both RAID arrays is the different vendor of the disks.

[jippie]

The problem is that the drive is automatically going into power save mode and spin up sometimes takes too long for md to believe the drive is still available. It therefore fails the drive.
To work around this, I created a small logical volume on the raid set, to which i write a few kB every five minutes from cron. This write is really fast and it simply prevents the drives from spinning down.

Would still be nice though to be able to change the timeout setting, it is currently set to somewhere around 10 seconds ...