FreeBSD 9.0 hangs on heavy I/O
gpalmer at freebsd.org
Wed May 30 00:24:53 UTC 2012
On Tue, May 29, 2012 at 10:59:58PM +0200, Kees Jan Koster wrote:
> Dear Gary,
> >> # camcontrol devlist
> >> <WDC WD740ADFD-00NLR1 20.07P20> at scbus1 target 0 lun 0 (pass0,ada0)
> >> <WDC WD740GD-00FLC0 33.08F33> at scbus2 target 0 lun 0 (pass1,ada1)
> >> <WDC WD740GD-00FLC0 33.08F33> at scbus3 target 0 lun 0 (pass2,ada2)
> >> <OCZ SUMMIT VBM1801Q> at scbus4 target 0 lun 0 (pass3,ada3)
> >> <PepperC Virtual Disc 1 0.01> at scbus7 target 0 lun 0 (pass4,cd0)
> >> <PepperC Virtual Disc 2 0.01> at scbus8 target 0 lun 0 (pass5,cd1)
> > Check the SSD for its internal block size and make sure your filesystem
> > and partitions are aligned with the disk block size. Unless there
> > is something wrong with your SATA controller I'd expect a lot more than
> > 273 IOPS/sec and ~30MByte/sec from a SSD.
> Thank you for suggesting this. However, I recently went through my file systems to fix disk alignment. I ended up aligning them to 1M blocks, which raised the throughput from 6M/s to about 60-80MB/s which is what I am seeing today.
> # gpart show
> => 34 250069613 ada3 GPT (119G)
> 34 2014 - free - (1M)
> 2048 250067599 1 freebsd-ufs (119G)
> Do you think I need to revisit alignment?
I don't have the specific device you have, but looking at the test results
from a random site for the same drive and firmware, they got 465 random IOPS
for a 0.5KB block size and a lot more than 60-80MB/sec. I get 60-80MB/sec
from a WD green drive in a pure write situation (admitedly using ZFS),
so I'm a bit surprised you're seeing similar performance from your SSD,
although now I look at it, the drive appears to be an older model. It could
be that you're running into issues where the drive is working hard as
all the flash blocks need to be erased before reuse. You may get some
improvement if you tweak the filesystem block size to the SSD block size.
TRIM may also help if the drive supports it.
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