Problems with journal?

[fluffles.net]

Giulio Ferro wrote:
> Miroslav Lachman wrote:
>> Giulio Ferro wrote:
>>> Giulio Ferro wrote:
>>>
>>>> I'm experiencing very serious delay issues in 2 production servers.
>>>
>>> [...]
>>>
>>>>
>>>> I hope any of you can help me look in the right direction, and
>>>> point me to any further tests to try or tunable
>>>> to set...
>>>>
>>>> Thanks in advance.
>>>>
>>>
>>> I didn't receive any answer to this, so I'm guessing ufs journal
>>> is abandoned or there is no interest in supporting it in production
>>> environment.
>>> Anyway I removed it from my servers and reverted to standard UFS,
>>> so the problems disappeared.  I also tried zfs (the only other
>>> journaled
>>> filesystem available on freebsd). I didn't experiences the hanging
>>> behavior
>>> I did with journaled ufs, but it's considerably slower than standard
>>> ufs
>>> (1/2 slower writes, 1/10 slower reads)...
>>
>> I am using gjournal on few production machines (not heavily IO
>> loaded) without any hangs.
>
> I'm glad for you. Unfortunately, as I reported in my original message, if
> the filesystem is cluttered enough even a simple "find" command can
> very nearly freeze the system.

Hi Giulio,

Have you checked that your disks or array is not using PIO mode? Which
uses hefty interrupts which will bring any system to its knees even on
light I/O.
For ata devices use atacontrol mode <disk> for scsi devices including
hardware RAID lookup dmesg. I'm not sure if hardware RAID can use PIO,
but any hybrid RAID / Fake RAID can.

Also, during the journal commit, you may experience a delay. Could you
provide some benchmarks like bonnie on the volume, without background
I/O if possible.

Not sure if any of this is related to your problem, though.

Kind regards,
Veronica