From: Jens Axboe <qemu@kernel.dk>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] Ensuring data is written to disk
Date: Tue, 1 Aug 2006 12:45:41 +0200 [thread overview]
Message-ID: <20060801104539.GO31908@suse.de> (raw)
In-Reply-To: <20060801101743.GA31760@mail.shareable.org>
On Tue, Aug 01 2006, Jamie Lokier wrote:
> > Of course, guessing the disk drive write buffer size and trying not to kill
> > system I/O performance with all these writes is another question entirely
> > ... sigh !!!
>
> If you just want to evict all data from the drive's cache, and don't
> actually have other data to write, there is a CACHEFLUSH command you
> can send to the drive which will be more dependable than writing as
> much data as the cache size.
Exactly, and this is what the OS fsync() should do once the drive has
acknowledged that the data has been written (to cache). At least
reiserfs w/barriers on Linux does this.
Random write tricks are worthless, as you cannot make any assumptions
about what the drive firmware will do.
--
Jens Axboe
next prev parent reply other threads:[~2006-08-01 10:45 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-08-01 0:11 [Qemu-devel] Ensuring data is written to disk Armistead, Jason
2006-08-01 10:17 ` Jamie Lokier
2006-08-01 10:45 ` Jens Axboe [this message]
2006-08-01 14:17 ` Jamie Lokier
2006-08-01 19:05 ` Jens Axboe
2006-08-01 21:50 ` Jamie Lokier
2006-08-02 6:51 ` Jens Axboe
2006-08-02 13:28 ` Jamie Lokier
2006-08-02 15:56 ` Bill C. Riemers
2006-08-07 13:11 ` R. Armiento
2006-08-07 16:14 ` Bill C. Riemers
2006-08-07 18:13 ` Thomas Steffen
2006-08-08 2:37 ` R. Armiento
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