On 13 November, 2006 - Eric Kustarz sent me these 2,4K bytes:
> Tomas Ögren wrote:
> >On 13 November, 2006 - Sanjeev Bagewadi sent me these 7,1K bytes:
> >>Regarding the huge number of reads, I am sure you have already tried
> >>disabling the VDEV prefetch.
> >>If not, it is worth a try.
> >That was part of my original question, how? :)
>
> On recent bits, you can set 'zfs_vdev_cache_max' to 1 to disable the
> vdev cache.
On earlier versions (snv_48), I did similar with ztune.sh[0], adding
cache_size which I set to 0 (instead of 10M).
This helped quite a lot, but there seems to be one more level of
prefetching..
Example:
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
ftp 1.67T 2.15T 1.26K 23 40.9M 890K
raidz2 1.37T 551G 674 10 22.3M 399K
c4t0d0 - - 210 3 3.19M 80.4K
c4t1d0 - - 211 3 3.19M 80.4K
c4t2d0 - - 211 3 3.19M 80.4K
c5t0d0 - - 210 3 3.19M 80.4K
c5t1d0 - - 242 4 3.19M 80.4K
c5t2d0 - - 211 3 3.19M 80.4K
c5t3d0 - - 211 3 3.19M 80.4K
raidz2 305G 1.61T 614 12 18.6M 491K
c4t3d0 - - 222 5 2.66M 99.1K
c4t4d0 - - 223 5 2.66M 99.1K
c4t5d0 - - 224 5 2.66M 99.1K
c4t8d0 - - 190 5 2.66M 99.1K
c5t4d0 - - 190 5 2.66M 99.1K
c5t5d0 - - 226 5 2.66M 99.1K
c5t8d0 - - 225 5 2.66M 99.1K
---------- ----- ----- ----- ----- ----- -----
Before this fix, the 'read bandwidth' for disks in the first raidz2
added up to way more than the raidz2 itself.. now it adds up correctly,
but some other readahead causes a 1-10x factor too much, mostly hovering
around 2-3x.. before it was hovering around 8-10x..
[0]:
http://blogs.sun.com/roch/resource/ztune.sh
/Tomas
--
Tomas Ögren, [EMAIL PROTECTED], http://www.acc.umu.se/~stric/
|- Student at Computing Science, University of Umeå
`- Sysadmin at {cs,acc}.umu.se
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