Date: Sun, 17 Apr 2005 13:10:24 -0600 From: Scott Long <scottl@samsco.org> To: Mikhail Teterin <mi+kde@aldan.algebra.com> Cc: msmith@mu.org Subject: Re: speed of a ciss-based pseudo-disk Message-ID: <4262B4A0.8080902@samsco.org> In-Reply-To: <200504171439.14530@aldan> References: <200504171439.14530@aldan>
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Mikhail Teterin wrote: > Hello! > > I have two U320 SCSI drives in a RAID-0 combination attached to HP's > Smart Array 642. This is the dmesg: > > ciss0: <HP Smart Array 642> port 0xb800-0xb8ff mem > 0xfea80000-0xfeabffff,0xfeafe000-0xfeafffff irq 29 at device 1.0 on pci4 > da0 at ciss0 bus 0 target 0 lun 0 > da0: <COMPAQ RAID 0 VOLUME OK> Fixed Direct Access SCSI-0 device > da0: 135.168MB/s transfers > da0: 69419MB (142171680 512 byte sectors: 255H 32S/T 17423C) > > Why is the reported speed only 135.168MB/s? All equipment is U320, so > I'd expect the nominal speed of 320MB/s... > > Should I try a different cable? Mine says U320, although the terminator > is marked U160 -- but 135 is not even 160... > > Any ideas? > Just because a disk can communicate at Ultra320 doesn't mean that it can sustain data at that rate. Same goes for ATA133 and SATA150. A typical modern disk can sustain about 50-70MB/s, and that's it. The fact that you're getting 135MB/s on a 2 disk sets completely validates this. What Ultra320 gives you is the ability to sustain that 50-70MB/s on multiple disks at once. Scott
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