I have four disks, of which two are WD15EARS, in a server and I'm trying to put the two WD15EARS's in Linux mdadm RAID, but for some reason, the array's performance is very slow (it syncs at about 15 MB/s). At first I thought it was an alignment issue, since they're Advanced Format drives, but I don't think so. This is how I aligned them. I also have two of these drives in my desktop PC, aligned painstakingly with LVM and RAID, and they're running fine.
I did some speed tests on the individual drives (sdb and sdd).
Hdparm -t shows 80 MB/s for sdb and only 30 MB/s for sdd (and the two other drives, two Samsung ones, measure at about 100 MB/s). These results are repeatable. It also shows that it's not an alignment thing, because then
hdparm -t would be slow on both drives.
I have been unable to discern any differences that might explain why one of these drives is slower, except that SMART reports the following on the good drive:
Offline data collection status: (0x82) Offline data collection activity was completed without error. Auto Offline Data Collection: Enabled.
And it reports this on the bad drive:
Offline data collection status: (0x85) Offline data collection activity was aborted by an interrupting command from host. Auto Offline Data Collection: Enabled.
The auto offline data collection should run every four hours, but the status message on the bad drive never changes.
I hypothesized that it's this offline collection that causes slowdown, but I am unable to abort it.
Smartctl -X doesn't do anything, which makes sense, because the drives do not have the "Abort Offline collection upon new command" capability, according to
I'm currently running a long self test which hopefully yields something, but in the meantime, I was hoping if anybody knows what might be going on.
Edit: the self test finished, it says it's OK. Turning off automatic offline data collection also didn't help.
And, I just did DD write tests.
dd if=/dev/zero of=/dev/sdX bs=10M yieled 65 MB/s on the good disk and about 15 MB/s on the bad one. There's definitely something wrong.
Edit2: I picked up the drives from the datacenter and connected it to my PC with a USB to SATA converter. Now it works fine...