From: "Jörn Engel" <joern@logfs.org>
To: Frantisek Rysanek <Frantisek.Rysanek@post.cz>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [noob q. on block layer] block IO read-ahead during sequential *write*?
Date: Mon, 7 Jan 2008 13:49:52 +0100 [thread overview]
Message-ID: <20080107124952.GA8201@lazybastard.org> (raw)
In-Reply-To: <47822835.4182.1ADF8AE7@localhost>
On Mon, 7 January 2008 13:25:09 +0100, Frantisek Rysanek wrote:
>
> let me start with a simple example. The following commands:
>
> cp /dev/zero /dev/hda
> dd if=/dev/zero of=/dev/hda [bs=512]
>
> both have one common side-effect: apart from the disk being properly
> overwritten with zeroes, the kernel seems to keep reading sectors
> ahead of the current seek position of the sequential write.
Block devices are cached in the page cache. If you write less than a
full page, any remainder has to be read from the device.
If you retry the dd with bs=4096 (or whatever your architecture's page
size happens to be), does this still occur?
Jörn
--
Chance favors only the prepared mind.
-- Louis Pasteur
next prev parent reply other threads:[~2008-01-07 12:55 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-07 12:25 [noob q. on block layer] block IO read-ahead during sequential *write*? Frantisek Rysanek
2008-01-07 12:49 ` Jörn Engel [this message]
2008-01-07 15:51 ` Frantisek Rysanek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20080107124952.GA8201@lazybastard.org \
--to=joern@logfs.org \
--cc=Frantisek.Rysanek@post.cz \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox