From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from frost.carfax.org.uk ([85.119.82.111]:58846 "EHLO frost.carfax.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752730AbaAUQwY (ORCPT ); Tue, 21 Jan 2014 11:52:24 -0500 Date: Tue, 21 Jan 2014 16:52:00 +0000 From: Hugo Mills To: Austin S Hemmelgarn Cc: Sandy McArthur , Toggenburger Lukas , "linux-btrfs@vger.kernel.org" Subject: Re: Working on Btrfs as topic for master thesis Message-ID: <20140121165200.GF3314@carfax.org.uk> References: <8E968DF3B7EC0D40B67B5A9D25675A6A03FC70@MBXSRV03EDU.edu.local> <52DD148E.3060200@gmail.com> <52DE6747.4050404@gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="udcq9yAoWb9A4FsZ" In-Reply-To: <52DE6747.4050404@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: --udcq9yAoWb9A4FsZ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Jan 21, 2014 at 07:25:43AM -0500, Austin S Hemmelgarn wrote: > On 2014-01-21 01:42, Sandy McArthur wrote: > > On Mon, Jan 20, 2014 at 7:20 AM, Austin S Hemmelgarn > > wrote: > >> > >> On 2014-01-16 14:23, Toggenburger Lukas wrote: > >>> 3. Improving subvolume handling regarding taking recursive snapshots ( https://btrfs.wiki.kernel.org/index.php/Project_ideas#Take_recursive_snapshots ) and taking snapshots of arbitrary directories ( https://btrfs.wiki.kernel.org/index.php/Project_ideas#Snapshot_arbitrary_directories ) > >> > >> Another option that I would personally love to see would be support for > >> write-mostly devices (that is, devices in a RAID1/RAID10 setup that only > >> get written too unless the data can't be found elsewhere). This would > >> in particular provide an alternative to using bcache/dm-cache (namely an > >> SSD and HDD in RAID1 with the HDD set to write-mostly). > >> Based on the current development focus, I don't think anybody is working > >> on this already (I would be, but I don't have either the time or the > >> skills with kernel programming that would be needed). > > > > Maybe this happens already: Might a similar effect be automatically > > achieved by tracking per-device I/O load averages and distributing > > reads based on the I/O loads of possible read devices? > > > That might be the case, it depends on how the I/O load averages are > calculated. I actually hadn't realized BTRFS did this, I thought it > behaved more like MD RAID (that is, distributing the reads among devices > in a un-weighted round-robin fashion). I think David tried that a while ago, and the benchmarks were actually worse. I'm not sure how much investigation he did into why, though. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Quidquid latine dictum sit, altum videtur. --- --udcq9yAoWb9A4FsZ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.15 (GNU/Linux) iQIVAwUBUt6lr1heFHXiqx3kAQL9fxAAjZtaT/EE1L7lFYxTkugRj7v/c3pFDffh 2x9hY9S97ZppGMI0CYbLT7FV9mnPOT3XnmJgoEIYF4Y3X9w+uHIY0Ylqnhx2Bzvz 4pWXbYZjyxZg0yxRItWrLfgOsxejKYnBdXQw4bmxVWapaZnRPbfhPFr4vC34uOIJ WtE/8/JR/VBBOxQwuaad3hQORxwvPZvPZy0DacMGTlHAKxodibJz+OJ6PWVmhX0O qhO/iZHk5dZM3/ifkMp9Se5q4xwy7JGyEHutSKoBXE/md371KGb4KB6clgPVgnPS BxBT1DSpyJuL9yk1sAb3TEHXpKTEaxHI52Lxf0bFLSUZ63IKZV6vX+i8Rj5JivbU KsF8ed8FNuze6GBsdw9ZX1UYXDE2eAQLJVoftzMN+KMutrLgxLR4ktKFIK9j8AkR qqaLkjPeH6NAFhX+ffUxcHYsnLvtj8jn4XnziGJqg2IkS6JrFS+/UJRSZ25h8nAQ Net/HAhf6reBK1GOPcheJnNU/IIcLoguhMEouw+k6V3jUekZpH2W270CuOJDj6eK xFtgcN1xXVZ1WdkRkulCYbZzbkn/tVIEny0pGJdzzEoVeo1Y/yxstkbmo0jaKCjS 5CYn+Vxs86fiNY7osI7gAAgLjWBfuyDFH3SiEdLXi56ur6cjikXR3VRu5gmRa0LZ Lolpjr58daA= =yoI9 -----END PGP SIGNATURE----- --udcq9yAoWb9A4FsZ--