On Mon, 27 Sep 2004 22:55:59 +0800, Winelfred G. Pasamba <[EMAIL PROTECTED]> wrote: .. > a 320mb/s controller can have about 10 15krpm disks each having > sustained 30mbps bandwidth. am i right? > > how about the pci bus? 66mhz is some 6mBps for 1bit bus. so 192mB/s > for 32bit and 384mB/s for 64bit. from my lousy computations, it looks > like 10 disks, u320, and 64bit pci are a balanced io match. for some > 320 mbps or mBps ba? tama ba iniisip ko?
Common fallacy. You are never gonna get a sustained 30Mbps per disk. Try something like... 800kbytes/second per disk. We've been over this uncounted times: the "common" disk access is about 1 block accessed at a time. Since a typical disk can do ~100 seeks per second (10ms random seek time) then 100 seeks X 8kbytes per block = 800kbytes/second. The sustained speed of the drive is only obtained when e.g. you're copying an ISO from one disk to another. But if you're randomly writing all over the disk (remember: writing ONE record in your database is around 4 seeks: seek to DB index to find offset, seek to offset to write data, seek back to DB index to update index, seek to journal to update journal). So obviously you're not going to get anywhere near the maximum data transfer speed of the drive, because the head is skating here and there across the disk platter and writing small amounts of data. Translation: even a 24-disk U320 SCSI array is not gonna saturate your typical PCI bus, or even an ultra-wide (40Mbit) SCSI bus. -- 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
