On 12/18/2010 12:00 AM, Lamar Owen wrote: > On Friday, December 17, 2010 06:14:31 pm Terry Barnaby wrote: >> The two main RAID1 disks are WD10EARS (Green). I have seen reported some >> issues with the performance of these but in my case they appear to work >> fine when the system is running ok. > [snip] >> Anyone seen this sort of behaviour before ? >> Any ideas one where to look ? > > Yes, I have. > > Use a different drive. Use iostat -x 1 to trace which disk in the RAID1 is causing problems; you'll likely find that the WD10EARS are throwing long awaits. Rumor is that this is by design; WD has enterprise 'RAID ready' drives and don't rate the lower priced drives for RAID. I have a WD15EADS that does this. At least the EARS version can possibly be put in a 'TLER' mode that allows RAID use. > > In my case, I had the WD15EADS drive as one half of a RAID1, with the other half being a Seagate 1.5TB drive of the same LBA. Every once in a while, performance would absolutely go to pot, and stay that way for minutes at a time (load averages>10 on a single core system). Using iostat -x 1 I was able to isolate the issue to that particular drive (I swapped controller channels, swapped cables, swapped out the power supply, swapped to a different controller chip on the motherboard, swapped motherboards, and the issue was always on this drive). > > When I replaced the WD15EADS with another Seagate 1.5TB, performance came back to normal. I'm using the WD15EADS in a single mode, now, with much lighter usage, and realizing that performance is not its strong suite. > > Also, the EARS version might use 4K sectors, exposing 512 byte sectors in an 'emulation' mode; properly aligning partitions to 4K boundaries solves that. > > Google 'WD EARS TLER' and get the whole story. You'll also want to disable the 'green' mode, as that will also negatively impact performance. There are tools out there to do that. Thanks for the info. I did play with setting a partition on a 4096 byte (8 x 512Byte sector) boundary, but saw no change in random 512Byte block write speed with a simple test program. These are recent drives so I wondered if things had changed in this regard. It is strange, however, how the system can run perfectly fine with good fast disk IO for a while and then go into this slow mode. In the slow mode a command can take 30seconds or more to run on an unloaded system. It smacks of some Linux kernel SATA driver/RAID1 versus WD EARS drive interaction to me. However, I think I will change the drives. I was hoping to try some WD10EADS ones I have, but after your issues I will look at the RE series or another make ... Cheers Terry -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
