Date: Tue, 7 Dec 1999 10:09:47 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Justin T. Gibbs" <gibbs@FreeBSD.ORG> Cc: Mike Smith <msmith@FreeBSD.ORG>, Julian Elischer <julian@whistle.com>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern kern_shutdown.c Message-ID: <199912071809.KAA30408@apollo.backplane.com> References: <199912071504.IAA00354@caspian.plutotech.com>
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:Remember that softupdates doesn't care if the drive does write behind so
:long as it only acknowledges that the write has completed once the drive
:can guarantee it will hit the platters. Usually this means that it has
:been written, but it may mean that the head is on cylinder and that the
:data can be written (barring a media failure) even if power is lost.
:You should get this behavior if you disable write caching on the disk,
:and with tagged queuing, the drives firmware should still have plenty
:of information to sort how it clears its write buffer.
:
:--
:Justin
I just realized --- softupdates doesn't use the ordered tag at all.
It only issues writes for buffers that can be written out of order,
then waits for the SCSI command to complete before issuing the
dependancies.
-Matt
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