From: Christoph Hellwig <hch@infradead.org>
To: Sage Weil <sage@inktank.com>
Cc: elder@inktank.com, Mike Snitzer <snitzer@redhat.com>,
Ugis <ugis22@gmail.com>,
linux-lvm@redhat.com,
"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>,
"ceph-users@ceph.com" <ceph-users@ceph.com>
Subject: Re: [linux-lvm] poor read performance on rbd+LVM, LVM overload
Date: Mon, 21 Oct 2013 07:11:47 -0700 [thread overview]
Message-ID: <20131021141147.GA30189@infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.00.1310202051240.29488@cobra.newdream.net>
On Sun, Oct 20, 2013 at 08:58:58PM -0700, Sage Weil wrote:
> It looks like without LVM we're getting 128KB requests (which IIRC is
> typical), but with LVM it's only 4KB. Unfortunately my memory is a bit
> fuzzy here, but I seem to recall a property on the request_queue or device
> that affected this. RBD is currently doing
Unfortunately most device mapper modules still split all I/O into 4k
chunks before handling them. They rely on the elevator to merge them
back together down the line, which isn't overly efficient but should at
least provide larger segments for the common cases.
next prev parent reply other threads:[~2013-10-21 14:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-16 14:46 [linux-lvm] poor read performance on rbd+LVM, LVM overload Ugis
2013-10-16 16:16 ` Sage Weil
2013-10-17 9:06 ` David McBride
2013-10-17 15:18 ` Mike Snitzer
2013-10-18 7:56 ` Ugis
2013-10-19 0:01 ` Sage Weil
2013-10-20 15:18 ` Ugis
2013-10-20 18:21 ` [linux-lvm] [ceph-users] " Josh Durgin
2013-10-21 3:58 ` [linux-lvm] " Sage Weil
2013-10-21 14:11 ` Christoph Hellwig [this message]
2013-10-21 15:01 ` Mike Snitzer
2013-10-21 15:06 ` Mike Snitzer
2013-10-21 16:02 ` Sage Weil
2013-10-21 17:48 ` Mike Snitzer
2013-10-21 18:05 ` Sage Weil
2013-10-21 18:06 ` Christoph Hellwig
2013-10-21 18:27 ` Mike Snitzer
2013-10-30 14:53 ` Ugis
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