From: Jens Axboe <axboe@kernel.dk>
To: Hiroyuki Yamada <mogwaing@gmail.com>
Cc: "Andrey Kuzmin" <andrey.v.kuzmin@gmail.com>,
"Georg Schönberger" <gschoenberger@thomas-krenn.com>,
fio@vger.kernel.org
Subject: Re: I/O is issued twice at scsi level
Date: Mon, 03 Dec 2012 19:33:42 +0100 [thread overview]
Message-ID: <50BCF086.8040105@kernel.dk> (raw)
In-Reply-To: <CAPDOW77MYSa8goV12f4A+RusQSgnP0hcw5GBD-a6D+VztkGmPw@mail.gmail.com>
On 2012-12-03 18:09, Hiroyuki Yamada wrote:
> Sorry for update.
> I figured it out.
> It's from ext3's indirect block mapping.
> There is one mapping block in each 1024 blocks,
> so accessing a large file randomly has high chance of accessing the
> mapping block and the requested block.
>
> Ext4 has different and more efficient addressing called extent (tree), and
> we can avoid the issue.
Ah, yes that makes sense. I thought we were talking about extra writes,
but it seems I misread the log since it clearly states FROM_DEVICE
transfers.
--
Jens Axboe
prev parent reply other threads:[~2012-12-03 18:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-01 8:31 I/O is issued twice at scsi level Hiroyuki Yamada
2012-12-01 14:26 ` Georg Schönberger
2012-12-01 14:51 ` Hiroyuki Yamada
2012-12-02 9:23 ` Hiroyuki Yamada
2012-12-03 13:43 ` Jens Axboe
2012-12-03 13:59 ` Andrey Kuzmin
2012-12-03 17:09 ` Hiroyuki Yamada
2012-12-03 18:33 ` Jens Axboe [this message]
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