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From: John Baldwin <jhb@freebsd.org>
To: rihad <rihad@mail.ru>
Subject: Re: mfi timeouts
Date: Wed, 27 Feb 2013 11:59:13 -0500
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Cc: freebsd-stable@freebsd.org, vince@unsane.co.uk
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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.

-- 
John Baldwin