Jeremy Chadwick wrote:
On Fri, Jul 25, 2008 at 09:46:34AM +0200, Claus Guttesen wrote:
Hi.
I installed FreeBSD 7 a few days ago and upgraded to the latest stable
release using GENERIC kernel. I also added these entries to
/boot/loader.conf:
vm.kmem_size="1536M"
vm.kmem_size_max="1536M"
vfs.zfs.prefetch_disable=1
Initially prefetch was enabled and I would experience hangs but after
disabling prefetch copying large amounts of data would go along
without problems. To see if FreeBSD 8 (current) had better (copy)
performance I upgraded to current as of yesterday. After upgrading and
rebooting the server responded fine.
With regards to RELENG_7, I completely agree with disabling prefetch.
The overall performance (of the system and disk I/O) appears signicantly
"smoother", e.g. less hard lock-ups and stalls, is better when prefetch
is disabled.
FYI I do not get "lock-ups" when running with prefetch. It is supposed
to just affect performance, i.e. if you have few disks or they have low
bandwidth or high seek times (e.g. crappy ATA) then it can saturate them
and you will have poor response times. However if your hardware is more
capable then it is a performance optimization.
Someone needs to obtain the usual debugging information.
Kris
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