Date: Sat, 13 Oct 2001 00:37:09 +0200 (MET DST) From: Alexey Koptsevich <alex@astro.su.se> To: Scott Long <scott_long@btc.adaptec.com> Cc: scsi@freebsd.org Subject: Adaptec 3210S: RAID5 performance and bus throughput Message-ID: <Pine.GSO.4.10.10110122310180.12138-100000@dioscuri.astro.su.se> In-Reply-To: <20011011123557.A406@hollin.btc.adaptec.com>
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Hello, > > Also, how many discs can I put to a channel and avoid decreasing > > performance? I think, if modern disk is able to transfer 30 Mb/s only 5 > > disks can be put to one channel, so 10 disks is practical limit for > > 2-channel Ultra160 controller. But it is only an idea, what does follow > > from the experience? > > It follows the law of dimishing returns. Every disk that you add will > increase performance my a lower factor than the previous. You also > have to remember that performace is also based on the PCI bus and > the CPU on the controller. If the card is only in a PCI 33MHz/32Bit > slot, you can only get 132MB/s max (actually much less than that in > real life). Since the bus is real bottleneck, I wonder what is the purpose to have 4-channel RAID controllers, in principle? Just to connect many discs? I mean, 4-channel controller gives 160*4=640Mb/s, but this cannot be driven even by 64bit/66MHz bus which provides only 528Mb/s! Also, are there x86 motherboards which provide those 64bit/66MHz? I also wonder what is real performance of 3210S in RAID5 mode? Are 4-5 disks which saturate 160Mb/s on SCSI bus (assume that load is heavy) are able to saturate those 132Mb/s on PCI bus after performing all XOR calculations? If not, how many discs saturate 132Mb/s? And, as a conclusion from previous question, is there real purpose to have 2-channel controller on 32bit/33MHz PCI (which is used on my Intel L440GX, assuming its 66MHz PCI to be weak), using it in RAID5 mode? Thanks a lot, Alex To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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