Date: Sun, 15 Mar 1998 18:30:34 -0800 (PST) From: Simon Shapiro <shimon@simon-shapiro.org> To: Cory Kempf <ckempf@enigami.com> Cc: "scsi@freebsd.org" <scsi@FreeBSD.ORG>, Raul Zighelboim <rzig@gulfsouth.verio.net> Subject: RE: to raid or not to raid Message-ID: <XFMail.980315183034.shimon@simon-shapiro.org> In-Reply-To: <v04003a27b1322c3fa095@[208.140.182.45]>
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On 16-Mar-98 Cory Kempf wrote: > At 19:44 -0500 98.03.15, Raul Zighelboim wrote: >>My missing link is: >> >>Will a (7 drive array under raid 5) be faster than a sinlg larger drive >>?... >> Will it be as fast as a (5 drive raid 5 array) ? >> > > As it stands, the question is meaningless: it depends on the drives and > the > controllers. > > In general though, the more drives, the more overhead. IME, two drives > striped together (assuming the bus could handle the throughput) gave the > best performace. Beyond two drives, the command overhead started to show > up. > > I would expect that the 7 drive array would be slower than the 5 drive > array. On most systems, yes. > A pair of Cheetah drives, on either FC or UW SCSI will probably give > optimal performance. My experience with FCAL shows, with the proper RAID controller, many more drives than two, before the host starts seeing the degradation. FCAL is sort of expensive for most folks. > RAID 5 will cost performance. Slower disks will seriously cost > performance. More than two disks will cost performance. A single > Cheetah > will perform less well. Any other drive model (at the moment, tomorrow > the > answers will change :-) ) will cost performance. Slower controllers will > cost performance. Doing the XORs in software (rather than hardware) may > cost performance. Not may, will. Write yourself a little RAID-5 parity logic. It is easy to write. Very revealing... An important side to all this, again, is the disks, the cabinets, the cables, the rest of the system. Without good facilities to do true hot-spares, hot plug replacement, automatic recovery for failed devices, the benefit of RAID arrays is meaningless. Painful experience talking :-) ---------- Sincerely Yours, Simon Shapiro Shimon@Simon-Shapiro.ORG Voice: 503.799.2313 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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