Date: Fri, 26 Aug 2005 16:21:07 +0400 From: "Vasim Valejev" <vasim@human-capital.ru> To: "Scott Long" <scottl@samsco.org> Cc: freebsd-amd64@freebsd.org Subject: Re: Slow PCI-X controller perfomance (adaptec 2130SLP) Message-ID: <0e5c01c5aa38$a2c4bca0$2107a8c0@vasimwork> References: <00d601c5a88e$1cb8c260$2107a8c0@vasimwork> <4305F56C.8090405@samsco.org>
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Hi ! > Whenever people complain about slow performance with AAC products and > try to point the finger at the driver, I ask them do repeat their > benchmark under linux and see how it compares. Then they realize just > how good they have it with FreeBSD. I've worked very hard over the > years to make the FreeBSD driver be the fastest driver available for > AAC cards. Yep, you was right, FreeBSD was a lot faster. The linux (Fedora Core, 2.6.11 kernel) got slightly better read speed but writes were 2-3 times slower (about 20-24 MB/s with 64k stripe). Not sure if i did everything correctly under linux but that was really low. > Your particular test is testing the following things: > > 1) disk transfer speed > 2) controller firmware efficiency > 3) cache memory bandwidth on the controller > 4) stripe alignment of the requests > 5) PCI-X bandwidth > > Your disk transfer speed is going to be about 70MB/s per disk. Given > that you are doing RAID-5 on 4 disks, you'll ideally get 3x70MB/s = > 210MB/s. The reason that you multiply by 3 and not 4 is that for a > given stripe, you only have 3 disks that contain data, with the 4th > disk containing parity information. Also note that you are dealing > with Ultra320. Adding more disks than what you have will start to > saturate the bandwidth of the bus (which is probabl between 260-300MB/s > depending on a lot of factors) I've made RAID-5 array (64k stripe) with all six disks but didn't got better than 80..90 MB/s for 2GB file write (on /usr partition with bs=256k) and 133 MB/s read from raw device (first 2GB of /dev/aacd0 with bs=256k, turning off read caching doesn't make any difference). That isn't bad either, so i'll stay with that. But it looks like some kind of bandwidth limit somewhere. Vasim V.
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