HEADS UP: New ZFS in the tree.

Jeremy Chadwick koitsu at FreeBSD.org
Wed Nov 19 02:13:48 PST 2008

On Wed, Nov 19, 2008 at 11:48:17AM +0200, Nikolay Denev wrote:
> Hash: SHA1
> On 19 Nov, 2008, at 11:25 , Larry Rosenman wrote:
>> On Wed, 19 Nov 2008, Jeremy Chadwick wrote:
>>> Since this is CURRENT, you should be able to increase the kmem_size
>>> and kmem_size_max entries to something larger than 1536M, especially
>>> since the box has 4GB of RAM.  (You shouldn't do this on RELENG_7).
>>> You might also consider disabling prefetch; there are reports of
>>> peoples' boxes locking up hard (requiring a hard reset) when prefetch
>>> is enabled.  Others (like myself) just see "better overall system
>>> responsiveness" when prefetch is disabled.
>> Just as a note, with a -CURRENT from shortly after the ZFS upgrade,  
>> the vm.kmem* tuneables, without ANY override on my 4G amd64 box:
>> vm.kmem_size_scale: 3
>> vm.kmem_size_max: 4509713203
>> vm.kmem_size_min: 0
>> vm.kmem_size: 1381195776
>> this is with a 2T zfs array, if that matters.
>> -- 
>> Larry Rosenman                     http://www.lerctr.org/~ler
>> Phone: +1 512-248-2683                 E-Mail: ler at lerctr.org
>> US Mail: 430 Valona Loop, Round Rock, TX 78681-3893
> Well, it looks like that on -current and a 4G amd64 machine probably  
> there is no need
> to tune anything. Here are my defaults with everything vm and zfs  
> related in loader.conf commented :
> vm.kmem_size_max: 4509713203
> vfs.zfs.arc_max: 863907840

I've discussed ZFS tuning with another FreeBSD user 2-3 months ago.  I
lost 8 years worth of Email recently, so I can't go back and check who
he was and what exactly was said.

He was saying that under normal circumstances (in RELENG_7 and CURRENT),
tuning should not really be necessary.  He also pointed out that the way
we're tuning things (specifically the variables we're using) are
partially incorrect; some are unnecessary, such as arc_min.

I'll see if I can find the mail on a mailing list (I think it was a
public mail), but it'll take me some time.  The information in the mail
is very good, and should probably be pulled in to the ZFS Tuning wiki.

Give me a while to find it.

| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

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