8.0-RELEASE: disk IO temporarily hangs up (ZFS or ATA relatedproblem)

Johan Hendriks Johan at double-l.nl
Mon Dec 28 08:21:31 UTC 2009

>ZFS will write buffer ALOT.  Your settings of vfs.zfs.arc_min and
vfs.zfs.arc_max will likely affect how bursty this >is.  I've been
running with Min, 32 GB arc, and see very bursty writes (of course, my
systems have 64GB). 

>Also, use 'zpool iostat 1' and not the system iostat. Check gstat as

>also try using CAM_ATA (ahci.ko) instead of ad devices, so your can get
the benefits of tag queuing.

>There is also a possible undocumented issue with, I believe it was the
WD green drives, where the vibration of the >drive actually slowed it
down.  This was demonstrated by setting a pound or two of silly putty on
the top of the >drive, and its performance (significantly) increased.
Experiment with putting some heavily, non-conductive weight on >top of
each drive - a book or something. 

Even with hardware the FreeBSD Handbook comes Handy ;-) 

> ensure that is its securely mounted as well. 

>David P. Discher
>dpd at bitgravity.com * AIM: bgDavidDPD
>BITGRAVITY * http://www.bitgravity.com

>On Dec 18, 2009, at 12:04 PM, Alexander Zagrebin wrote:

>>>> The disks are used for mirrored ZFS pool.
>>>> I have noticed that the system periodically locks up on 
>>> disk operations.
>>>> After approx. 10 min of very slow disk i/o (several KB/s) 
>>> the speed of disk
>>>> operations restores to normal.
>>>> gstat has shown that the problem is in ad6.
>>> Want you try this patch and report?:
>>> http://people.freebsd.org/~attilio/lockmgr_lostwake.diff
>>> It should apply to STABLE_8 and if not, just report and I will help.
>> Thanks fo your attempt to help!
>> I've successfully applied this patch to RELENG_8_0, recompiled
>> kernel and required modules (krpc, opensolaris,zfs),
>> but nothing has changed. The problem still exist.
>> -- 
>> Alexander Zagrebin
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