Strange ZFS performance

[Jeremy Chadwick]

On Sun, Apr 04, 2010 at 11:18:45PM +0400, Mikle wrote:
> Hello, list!
> I've got some strange problem with one-disk zfs-pool: read/write performance for the files on the fs (dd if=/dev/zero of=/mountpoint/file bs=4M count=100) gives me only 2 MB/s, while reading from the disk (dd if=/dev/disk of=/dev/zero bs=4M count=100) gives me ~70MB/s. 
> pool is about 80% full; PC with the pool has 2GB of ram (1.5 of which is free); i've done no tuning in loader.conf and sysctl.conf for zfs. In dmesg there is no error-messages related to the disk (dmesg|grep ^ad12); s.m.a.r.t. seems OK.
> Some time ago disk was OK, nothing in software/hardware has changed from that day.
> Any ideas what could have happen to the disk?

Please provide the following output:

1) uname -a
2) sysctl kstat.zfs.misc.arcstats
3) smartctl -a /dev/ad12

Also, does rebooting the box restore write speed (yes, this is a serious
question/recommendation)?

-- 
| 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 |