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Subject: Re: 2.4.21-pre2 stalls out when running unixbench
From: "Stephen C. Tweedie" <sct@redhat.com>
To: John Bradford <john@grabjohn.com>
Cc: Andrew Morton <akpm@digeo.com>, joe.korty@ccur.com,
       Andreas Dilger <adilger@clusterfs.com>, rusty@rustcorp.com.au,
       riel@conectiva.com.br, linux-kernel@vger.kernel.org, hch@sgi.com,
       Stephen Tweedie <sct@redhat.com>
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Hi,

On Mon, 2003-01-06 at 12:15, John Bradford wrote:

> What!?  I'm suprised that no userspace applications were broken by
> sync returning before the data is safely on oxide, even though it
> doesn't violate the POSIX spec.

sync(2) syncs _everything_ --- every M/O or floppy disk, every
filesystem no matter if it's fat or native Unix.  It's way too
heavyweight for most applications which have synchronisation
requirements, when fsync() or O_SYNC are much more precise.

I think I can recall one or two mutterings about people worried about
theoretical risks of doing things like "lilo; sync; reboot", but that's
a different class of risk altogether.  (It's complicated by the problem
that after a sync, ext3 guarantees that the data and metadata is on
disk, but it may still be in the journal, so lilo won't necessarily see
the right stuff with sync() alone --- ext3 plays extra tricks when it
sees bmap to try to solve this.)

--Stephen

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