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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[-- Attachment #1 --] Michael Butler wrote: > I would think that journaling on one drive and storing the resultant > data-set on another would improve performance enormously (reduced > seek-lengths) and more so if they were 1) high-rpm drives (less > rotational latency) and 2) on different buses (no bus/controller > contention), There are (very near) limits to what you can do with such a setup: the drive that holds the external journal needs to be much faster than the 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 the file system. Ideally, the journal drive would have to deliver at least twice as sequential IO as the main drive to maximize the potential performance. Thus, using a conveniently small medium as an USB flash drive is not very useful (the high seek rate will remain unused and 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, and benefits a lot from the detached journal. Margins of errors are 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 [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFHplBNldnAQVacBcgRAuMyAJ0ce6nqja0lrkrGRAInm8Xn74fZVQCgsl5h +N3qni0MsBUnACGru8blBno= =RTXJ -----END PGP SIGNATURE-----home | help
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