Date: Wed, 27 Feb 2013 11:59:13 -0500 From: John Baldwin <jhb@freebsd.org> To: rihad <rihad@mail.ru> Cc: freebsd-stable@freebsd.org, vince@unsane.co.uk Subject: Re: mfi timeouts Message-ID: <201302271159.13424.jhb@freebsd.org> In-Reply-To: <512DA073.9090908@mail.ru> References: <512CFF90.8080806@mail.ru> <201302261548.56253.jhb@freebsd.org> <512DA073.9090908@mail.ru>
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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
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