8.2-RC1 and ZFS

[David Samms]

On 12/30/10 09:54, David Samms wrote:
> On 12/30/10 01:57, Marco van Tol wrote:
>> On Wed, Dec 29, 2010 at 05:11:32PM -0700, David Samms wrote:
>>> I gave ZFS a try again this afternoon and immediately came across what I
>>> would consider a problem. Simply running dd causes such IO contention
>>> that a GUI desktop is unusable and MP3s stop playing. The problem is
>>> very repeatable, just run dd if=/dev/zero of=big bs=1m count=6400
>>>
>>> System is amd64, source updated Dec 27. Default ZFS parameters. (no
>>> tuning). With the same system but UFS+s dd causes no problems.
>>
>> Check out this mail from Jeremy Chadwick from December 28th in
>> freebsd-stable at .
>> http://docs.freebsd.org/cgi/getmsg.cgi?fetch=312384+0+current/freebsd-stable
>>
>>
>> I think specifically the comments and tweaks regarding
>> vfs.zfs.txg.timeout="5" and vfs.zfs.txg.write_limit_override=1073741824
>> should be usefull for you. :-)
>>
>> I'm intentionally not touching the subject why you see what you do
>> without tuning. I'm sure there are a great bunch of different
>> situations for which the defaults are the way they are.
>>
>> :-)
>>
>> Marco van Tol
>>
>
> Marco, thank you for your reply. Jeremy, thank you for your tuning
> suggestions. It does appear that the default setting for ZFS are NOT
> well suited for a single drive setup. Based on Jeremy's suggestions I
> made the following changes from the defaults:
>
> vfs.zfs.txg.timeout="5"
> vfs.zfs.txg.write_limit_override=268435456 # (System has 4G of RAM)
> kern.maxvnodes=250000
>
> I tested both UFS+s and ZFS for desktop usability while running "dd" to
> create IO contention. System has two identical 300G WD drives that are
> about 4 years old. For testing I switch at boot between the drives, one
> is ZFS the other UFS+s. Test was performed using XFCE4 with xmms playing
> MP3s while "dd" was creating a large file and OpenOffice was launching.
>
> ZFS
> ----------------------------------------------------------------------
> %dd if=/dev/zero of=big bs=1m count=6400
> 6710886400 bytes transferred in 177.418146 secs (37825254 bytes/sec)
>
> openoffice startup about 185 sec
> No MP3 skips
> XFCE4 popup menus took 1-3 seconds to appear
>
> UFS+s
> ----------------------------------------------------------------------
> dd if=/dev/zero of=big bs=1m count=6400
> 6710886400 bytes transferred in 165.061623 secs (40656855 bytes/sec)
>
> openoffice startup about 185 sec
> No MP3 skips
> XFCE4 popup menus took 5-25 seconds to appear
>
> While dd IO was slower with the new ZFS parameters, the desktop was very
> usable, and its responsiveness was better than USF+s. I will be
> upgrading to ZFSv28 and repeating this rudimentary desktop usability test.

The same test with ZFSv28 and ZFSv28 + tuning

ZFSv28
----------------------------------------------------------------------
dd if=/dev/zero of=big bs=1m count=6400
6710886400 bytes transferred in 158.205268 secs (42418855 bytes/sec)

OpenOffice 197sec
MP3 skips
XFCE4 popup menus took 5-15 seconds to appear


ZFSv28 + tuning
--vfs.zfs.txg.timeout="5"
--vfs.zfs.txg.write_limit_override=268435456
--kern.maxvnodes=250000
----------------------------------------------------------------------
dd if=/dev/zero of=big bs=1m count=6400
6710886400 bytes transferred in 167.316444 secs (40108947 bytes/sec)

OpenOffice 190sec
No MP3 skips during "dd", but one skip while OpenOffice was starting
XFCE4 popup menus took 2-13 seconds to appear