Date: Mon, 04 Feb 2008 00:37:43 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-stable@freebsd.org Subject: Re: gjournal panic 7.0-RC1 Message-ID: <fo5j8e$96g$1@ger.gmane.org> In-Reply-To: <47A63610.4070608@protected-networks.net> References: <3aaaa3a0802030751w69ce59a9oeb869e3d87d92616@mail.gmail.com> <fo58j1$7hq$1@ger.gmane.org> <47A62B00.1060403@egr.msu.edu> <3aaaa3a0802031318y2e3fd33en8071c82172ab9ecf@mail.gmail.com> <47A63610.4070608@protected-networks.net>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigABE262E7FCBEA5D933381A10 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Michael Butler wrote: > I would think that journaling on one drive and storing the resultant=20 > data-set on another would improve performance enormously (reduced=20 > seek-lengths) and more so if they were 1) high-rpm drives (less=20 > rotational latency) and 2) on different buses (no bus/controller=20 > contention), There are (very near) limits to what you can do with such a setup: the=20 drive that holds the external journal needs to be much faster than the=20 data drive, since it will become the main bottleneck in IO. It has to be = faster mostly in sequential IO, seeks are only present when transferring = journal data to the main drives while under simultaneous write IO from=20 the file system. Ideally, the journal drive would have to deliver at=20 least twice as sequential IO as the main drive to maximize the potential = performance. Thus, using a conveniently small medium as an USB flash=20 drive is not very useful (the high seek rate will remain unused and=20 sequential performance is generally lower than regular drives) I've done some benchmarking. The setup is: three 7.5k RPM drives, two in = RAID0, one for the journal. Here's a summary of the results: UFS+SU: bonnie++: writes: 102 MB/s, rewrites: 47 MB/s, reads: 103 MB/s postmark: 110 trans/s UFS+GJ: bonnie++: writes: 35 MB/s, rewrites: 22 MB/s, reads: 99 MB/s postmark: 123 trans/s UFS+GJ-detached: bonnie++: writes: 46 MB/s, rewrites: 36 MB/s, reads: 100 MB/s postmark: 263 trans/s Postmark is configured to have a bias for writing a lot of small files,=20 and benefits a lot from the detached journal. Margins of errors are=20 around +/- 3 MB/s for bonnie++ and around 15 trans/s for postmark. For comparison, here are the results for Linux 2.6.23, regular ext3: bonnie++: writes: 105 MB/s, rewrites: 52 MB/s, reads: 128 MB/s postmark: 173 trans/s --------------enigABE262E7FCBEA5D933381A10 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFHplBNldnAQVacBcgRAuMyAJ0ce6nqja0lrkrGRAInm8Xn74fZVQCgsl5h +N3qni0MsBUnACGru8blBno= =RTXJ -----END PGP SIGNATURE----- --------------enigABE262E7FCBEA5D933381A10--
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