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?
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