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From: rihad <rihad@mail.ru>
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To: John Baldwin <jhb@freebsd.org>
Subject: Re: mfi timeouts
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On 02/27/2013 08:59 PM, John Baldwin wrote:
> On Wednesday, February 27, 2013 12:58:11 am rihad wrote:
>> Now about this part taken from here
>> http://lists.freebsd.org/pipermail/freebsd-scsi/2011-March/004839.html
>>   > By issuing a dummy read operation (thus forcing a flush of data
>> buffers), this issue is largely averted.
>>
>> Does this mean that battery-backed cache (BBU) is effectively rendered
>> useless, as all write operations are forced on to the disk platters on
>> every interrupt?
> No, this is a very different level.  This is forcing pending PCI DMA
> transactions on the PCI bus to flush by doing a read, not forcing I/O
> buffers to be flushed to disk.
>
Thanks for clarifying.

After applying the "dummy read" patch mfi timeouts don't appear in dmesg 
output any more, but i/o stalls still occurred 2-3 times during periods 
of high activity, for no more than 10-20 seconds. I guess the only way 
to fix that is to choose another hardware RAID implementation, or try 
Steven Hartland's patch? Does 8.3 or 9.1 include more fixes in this 
area, is upgrading recommended?