[zfs-discuss] zfs-discuss] Low read performance on ZFS based on iSCSI disk

Ruben Kelevra ruben at vfn-nrw.de
Wed Jan 13 12:10:12 EST 2016


Can you redo your dd with oflag=sync on write please?

Best regards Ruben 

> Am 13.01.2016 um 13:59 schrieb Dan Swartzendruber via zfs-discuss <zfs-discuss at list.zfsonlinux.org>:
> 
> I export a raid 10 4x2 using scst with zfs built from master from 4 months or so ago.  I swItched from zvol to files on a dataset due to performance that would deteriorate after some days.  Not the same exact symptoms, but clearly something was not right with zvols.  On a kindle right now, so this is vague.  If you would like more data, I can dig some up later?
> 
> kaazoo via zfs-discuss <zfs-discuss at list.zfsonlinux.org> wrote:
>> For further troubleshooting I exported 6 disks directly via iSCSI and
>> configured the following zpool:
>> 
>> pool: pool1
>> state: ONLINE
>> scan: none requested
>> config:
>> 
>>    NAME          STATE     READ WRITE CKSUM
>>    pool1         ONLINE       0     0     0
>>      mirror-0    ONLINE       0     0     0
>>        mpath132  ONLINE       0     0     0
>>        mpath133  ONLINE       0     0     0
>>      mirror-1    ONLINE       0     0     0
>>        mpath134  ONLINE       0     0     0
>>        mpath135  ONLINE       0     0     0
>>      mirror-2    ONLINE       0     0     0
>>        mpath136  ONLINE       0     0     0
>>        mpath137  ONLINE       0     0     0
>> 
>> 
>> I get good performance for write/read:
>> 
>> dd if=/dev/zero bs=1M count=102400 of=/pool1/test/testfile && sleep 5 &&
>> dd if=/pool1/test/testfile bs=1M of=/dev/null
>> 102400+0 records in
>> 102400+0 records out
>> 107374182400 bytes (107 GB) copied, 205.016 s, 524 MB/s
>> 102400+0 records in
>> 102400+0 records out
>> 107374182400 bytes (107 GB) copied, 199.504 s, 538 MB/s
>> 
>> 
>> So the problem with low read performance seems to only exist when the
>> iSCSI target is based on a zvol and not when raw disks are used.
>> 
>> 
>> Regards,
>> kaazoo
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