From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Benny Halevy <bhalevy@panasas.com>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-nfs@vger.kernel.org, nfsv4@ietf.org
Subject: Re: [nfsv4] layoutcommits and file layout
Date: Mon, 03 Jan 2011 09:40:11 -0500 [thread overview]
Message-ID: <1294065611.16812.8.camel@heimdal.trondhjem.org> (raw)
In-Reply-To: <4D21DB53.9050104@panasas.com>
On Mon, 2011-01-03 at 16:21 +0200, Benny Halevy wrote:
> On 2010-12-17 01:07, Christoph Hellwig wrote:
> > On Thu, Dec 16, 2010 at 11:21:21AM -0500, Matt W. Benjamin wrote:
> >> Hi,
> >>
> >> We have a files implementation which wants to receive LAYOUTCOMMIT when a client is finished with a layout. It was my clear understanding from rfc5661 that we could expect this behavior.
> >
> > Care to post it to the list?
> >
>
> I don't know what Matt's server is doing but the fundamental problem is
> manifested with extending a file with parallel DS writes.
> Assuming that the DS writes are executed in arbitrary order,
> exposing the file length before LAYOUTCOMMIT can cause
> a concurrent reader to read a hole. Although locking can
> solve this case, day-to-day applications that work well over
> local filesystem and legacy NFS may break because of this.
...and this differs from ordinary NFS writes exactly how?
Both cached and uncached (i.e. O_DIRECT) writes can and will be flushed
to disk in entirely random order when writing to the MDS. If you have a
parallel reader on another client (or even on the same client in the
case of O_DIRECT), and want it to see accurate data, then use locking.
If not, you will see holes and other strangeness.
IOW: There are no 'day-to-day applications that work well over legacy
NFS' that rely on this behaviour.
_______________________________________________
nfsv4 mailing list
nfsv4@ietf.org
https://www.ietf.org/mailman/listinfo/nfsv4
next prev parent reply other threads:[~2011-01-03 14:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <978693366.32.1292516428080.JavaMail.root@thunderbeast.private.linuxbox.com>
2010-12-16 16:21 ` [nfsv4] layoutcommits and file layout Matt W. Benjamin
[not found] ` <1740153586.34.1292516481789.JavaMail.root-DQa+Qhn4Z593Hjf6844flrbbgpPoC6wPvwx5bNz670MAvxtiuMwx3w@public.gmane.org>
2010-12-16 23:07 ` Christoph Hellwig
2011-01-03 14:21 ` Benny Halevy
2011-01-03 14:40 ` Trond Myklebust [this message]
2011-01-05 19:01 ` Benny Halevy
2011-01-05 19:04 ` Trond Myklebust
2011-01-05 19:14 ` Trond Myklebust
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=1294065611.16812.8.camel@heimdal.trondhjem.org \
--to=trond.myklebust@fys.uio.no \
--cc=bhalevy@panasas.com \
--cc=hch@infradead.org \
--cc=linux-nfs@vger.kernel.org \
--cc=nfsv4@ietf.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;
as well as URLs for NNTP newsgroup(s).