On Mon, 16 Feb 2004, ian sison (mailing list) wrote: .. > > translation.. with SCSI you can put at least 10 drives on a single > > controller, assuming the application has lots of small files and lots of > > random seek (true of Squid and email servers). > > True, but that discounts optimization done on the OS level as well the > firmware level which can induce more data to be sent to the bus than the > over all average 400K/second you mentioned.
Yes that's true, but in reality the optimizations don't result in a 100-fold increase of performance. and in SOME cases (e.g. running Oracle on Linux, which has no KAIO support in the stock kernel) you WILL be limited by the I/O's per second because a commit causes a flush which means the kernel can't optimize the I/O. On a "saner" load, I've actually done the following braindead benchmark: cd /filesystem2 time tar zxf /filesystem1/linux-2.4.24.tar.gz since you know how many files are contained in the tarball, and the total size (unzipped) of the thing, you can get a good idea of the overall performance of the drives. filesystem1 and filesystem2 have to be on separate drives. you can argue that CPU is also being used, but with a modern CPU the utilization for untar-ing and g-unzipping is small. wth this benchmark, i've found that the maximum I/O's per second max out at around 120, and the raw speed to the disk is around 4-6MB/sec. so that's a factor of 10 higher than my earlier figure, but still a factor of 10 less than the hardware platter speed. the only way (i've found) to get platter speed is by doing time dd if=/dev/zero of=/filesystem1/big_file bs=1M count=1000 :) which is a very contrived example that doesn't reflect a real work-load at all. bottom-line, two drives on an Ultra-Wide SCSI bus won't saturate the bus under any realistic work load. Maybe my "10" figure was too optimistic, but you CAN accommodate 10 drives easily. --- Orlando Andico <[EMAIL PROTECTED]> Mosaic Communications, Inc. -- Philippine Linux Users' Group (PLUG) Mailing List [EMAIL PROTECTED] (#PLUG @ irc.free.net.ph) Official Website: http://plug.linux.org.ph Searchable Archives: http://marc.free.net.ph . To leave, go to http://lists.q-linux.com/mailman/listinfo/plug . Are you a Linux newbie? To join the newbie list, go to http://lists.q-linux.com/mailman/listinfo/ph-linux-newbie
