I have three Dell Poweredge 2950's. One with RAID-5 on 5 disks and two with RAID-5 on 3 disks. The latter two started to have performance issues – very high IO delay. When I checked the RAID status I found out that they are doing a patrol read on one disk. Also there are no SMART errors or anything similar – the disks seem to be fine, but I only used them for one week, so I can't be sure about that.
Patrol Reads should not reduce IO performances too much, right? But I can't use those machines anymore. I rebooted one of them and it won't boot correctly because it can't finish some of the start jobs and it takes like 30 minutes until I get a shell. Also the patrol read started about 20 hours ago, so it should be done by now.
I don't have OMSA installed, so I can't do anything about it and I can't install it because the IO delay is too damn high.
So my questions are:
- Why does the Patrol Read render my systems unusable – but only two of my three machines?
- Why does the Patrol Read take so long? I know that it restarts when the system reboots. I only rebooted one machine, so the other one should have finished in time.
- How do I fix this? I guess I have to somehow stop the Patrol Read in order to do anything useful – like installing management software.
EDIT: The hard drives are Dell WD7502ABYS – so they are enterprise class disks.
Best Answer
It is quite strange: patrol read should only work when disks are idle.
I strongly suspect something other is at play here. Are you using desktop-grade disks? Maybe one or more disks have read problems and the read load cause firmware-dependant timeouts (ie when using disks without TLER or similar).
Can you post controller and disks specification and details?