On Sun, 24 Aug 2014 12:16:03 +1000 Tim Boundy <gigap...@gmail.com> wrote:
> Package: mdadm > Version: 3.3-2 > Severity: normal > Tags: upstream > > I have a RAID5 array using 4x 3TB WD Red drives. On occasion while writing to > the array, the write operation will stall. Using iostat, I can see that one > of the member disks shows >95% utilisation performing reads at approximately > 0.5MB/s. This stall usually takes about 10 seconds to recover, sometimes up > to > a minute. Lengthy stalls cause Samba network transfers to fail, shorter > stalls > are mostly harmless if not annoying. The SMART output for the offending > member > drive looks clean. I did notice that I can reliably reproduce the stall by > restarting the array - the first write operation appears to trigger it. I've > had the array running for over a year and I've only just started noticing > this > recently. All drives are using native SATA ports on the Asrock A75M-HVS > motherboard. > > > > # iostat during a write stall > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz > avgqu-sz await r_await w_await svctm %util > sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 > 0.00 0.00 0.00 0.00 0.00 0.00 > sdc 0.00 0.00 0.00 0.00 0.00 0.00 0.00 > 0.00 0.00 0.00 0.00 0.00 0.00 > sdd 0.00 0.00 135.00 0.00 540.00 0.00 8.00 > 0.98 7.23 7.23 0.00 7.23 97.60 > sde 0.00 0.00 0.00 0.00 0.00 0.00 0.00 > 0.00 0.00 0.00 0.00 0.00 0.00 > sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 > 0.00 0.00 0.00 0.00 0.00 0.00 > md0 0.00 0.00 135.00 0.00 540.00 0.00 8.00 > 0.00 0.00 0.00 0.00 0.00 0.00 That's very distinctive, isn't it! I cannot see the md driver causing this. My guess is that it is caused by the filesystem - which I see is ext4. Maybe on first write, the filesystem loads some tables off disk, and all the tables are on the first drive. It would be worth asking on ext3-us...@redhat.com.au http://www.redhat.com/mailman/listinfo/ext3-users NeilBrown
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