zfs performance degradation

Bob Healey healer at rpi.edu
Wed Sep 23 20:42:55 UTC 2015


That sounds similar to the issues I posted about 10 days ago, but my 
issues seem to be more time than capacity based and go away on reboot.  
I haven't had time to follow up on my thread due to more pressing issues 
at work involving Microsoft products, but its still on my TODO list.

Bob Healey
Systems Administrator
Biocomputation and Bioinformatics Constellation
and Molecularium
healer at rpi.edu
(518) 276-4407

On 9/22/2015 1:38 PM, Dmitrijs wrote:
> Goog afternoon,
>
>   I've encountered strange ZFS behavior - serious performance 
> degradation over few days. Right after setup on fresh ZFS (2 hdd in a 
> mirror) I made a test on a file 30Gb size with dd like
> dd if=test.mkv of=/dev/null bs=64k
> and got 150+Mbs speed.
>
> Today I got only 90Mbs, tested with different blocksizes, many times, 
> speed seems to be stable +-5%
>
> nas4free: divx# dd if=test.mkv of=/dev/null bs=64k
> 484486+1 records in
> 484486+1 records out
> 31751303111 bytes transferred in 349.423294 secs (90867734 bytes/sec)
>
>
>
> Computer\system details:
>
>  nas4free: /mnt# uname -a
> FreeBSD nas4free.local 10.2-RELEASE-p2 FreeBSD 10.2-RELEASE-p2 #0 
> r287260M: Fri Aug 28 18:38:18 CEST 2015 
> root at dev.nas4free.org:/usr/obj/nas4free/usr/src/sys/NAS4FREE-amd64 amd64
>
> RAM 4Gb
> I've got brand new 2x HGST HDN724040ALE640, 4Тб, 7200rpm (ada0, ada1) 
> for pool data4.
> Another pool, data2, performs slightly better even on older\cheaper WD 
> Green 5400 HDDs, up to 99Mbs.
>
>
>  nas4free: /mnt# zpool status
>   pool: data2
>  state: ONLINE
>   scan: none requested
> config:
>
>         NAME        STATE     READ WRITE CKSUM
>         data2       ONLINE       0     0     0
>           mirror-0  ONLINE       0     0     0
>             ada2    ONLINE       0     0     0
>             ada3    ONLINE       0     0     0
>
> errors: No known data errors
>
>   pool: data4
>  state: ONLINE
>   scan: none requested
> config:
>
>         NAME        STATE     READ WRITE CKSUM
>         data4       ONLINE       0     0     0
>           mirror-0  ONLINE       0     0     0
>             ada0    ONLINE       0     0     0
>             ada1    ONLINE       0     0     0
>
> errors: No known data errors
>
>
> While dd is running, gstat is showing like:
>
> dT: 1.002s w: 1.000s
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 0 366 366 46648 1.1 0 0 0.0 39.6| ada0
> 1 432 432 54841 1.0 0 0 0.0 45.1| ada1
>
>
>
> so iops are very high, while %busy is quite low. It averages about 
> 50%, rare peaks till 85-90%
>
> Even top shows no significant load:
>
> last pid: 61983; load averages: 0.44, 0.34, 0.37 up 11+07:51:31 16:44:56
> 40 processes: 1 running, 39 sleeping
> CPU: 0.3% user, 0.0% nice, 6.4% system, 1.1% interrupt, 92.1% idle
> Mem: 21M Active, 397M Inact, 2101M Wired, 56M Cache, 94M Buf, 1044M Free
> ARC: 1024M Total, 232M MFU, 692M MRU, 160K Anon, 9201K Header, 91M Other
> Swap: 4096M Total, 4096M Free
> Not displaying idle processes.
> PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
> 61981 root 1 30 0 12364K 2084K zio->i 3 0:09 18.80% dd
> 61966 root 1 22 0 58392K 7144K select 3 0:24 3.86% proftpd
>
>
>
> Zpool list:
>
>  nas4free: /mnt# zpool list
> NAME    SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP HEALTH ALTROOT
> data2  1.81T   578G  1.25T         -    11%    31%  1.00x ONLINE -
> data4  3.62T  2.85T   797G         -    36%    78%  1.00x ONLINE -
>
>
> Could it happen because of pool being 78% full? So I cannot fill puls 
> full?
> Can anyone please advice how could I fix the situation - or is it normal?
> I've googled a lot about vmaxnodes, vminnodes but advices are mostly 
> controversial and doesn't help.
> I can provide additional system output on request.
>
> best regards,
> Dmitry
>
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