From owner-freebsd-questions Thu Mar 9 20: 9: 0 2000 Delivered-To: freebsd-questions@freebsd.org Received: from mojave.worldwide.lemis.com (mojave.lemis.com [192.109.197.162]) by hub.freebsd.org (Postfix) with ESMTP id 564CD37B804 for ; Thu, 9 Mar 2000 20:08:53 -0800 (PST) (envelope-from grog@mojave.worldwide.lemis.com) Received: (from grog@localhost) by mojave.worldwide.lemis.com (8.9.3/8.9.3) id SAA00454; Tue, 7 Mar 2000 18:20:29 +1100 (EST) (envelope-from grog) Date: Tue, 7 Mar 2000 18:20:29 +1100 From: Greg Lehey To: Mike Tancsa Cc: James , questions@FreeBSD.ORG Subject: Re: RAID/config questions Message-ID: <20000307182029.C331@mojave.worldwide.lemis.com> Reply-To: Greg Lehey References: <38c48132.1056418179@mail.sentex.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0i In-Reply-To: <38c48132.1056418179@mail.sentex.net>; from mike@sentex.net on Tue, Mar 07, 2000 at 04:15:35AM +0000 WWW-Home-Page: http://www.lemis.com/~grog X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF 13 24 52 F8 6D A4 95 EF Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-41-739-7062 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Tuesday, 7 March 2000 at 4:15:35 +0000, Mike Tancsa wrote: > On 6 Mar 2000 20:11:24 -0500, in sentex.lists.freebsd.questions you wrote: >> 1. What is the best RAID controller/model to use? (for either setup) >> I've been pretty happy with Adaptec and FreeBSD's support of Adaptec >> controllers, so I would prefer to stay with Adaptec but don't know about >> their RAID offerings.. > > No Adaptec RAID support. Try a Mylex DAC 960 based card for low end > or the AMI MegaRAID. Its pretty straightforward to setup via the > card's BIOS. I thought we were going to introduce both Mylex and Adaptec support for 4.0, but I believe Mike Smith is also adding some of this to -CURRENT. I don't know which one to recommend, but the supported DPT boards are rather out of date. >> 2. Which will give me better performance? RAID or RAID5? I know >> RAID5 will give me more disk space, but is there any significant >> i/o performance cost? Yes. RAID-5 has approximately the same performance as RAID-0 for reading, and approximately 1/4 of the performance for writing. Depending on the configuration, RAID-1 may give better performance than RAID-0 for reading. In all cases, stripe sizes are a key factor for performance. There's an interaction between stripe size and cylinder group size for ufs; you should attempt to spread the super blocks eaually over all components of the volume. This isn't easy. I've written a program to guesstimate it, but I don't have any hard measurements to back up the figures. Also, a large stripe size (256 kB) *should* be optimal, but some RAID controllers seem to have limitations in their implementation that make smaller stripes more appropriate (and limit the performance of the controller). >> And generally speaking, how much of a performance degredation may I >> see (if any) in going from a non-raid SCSI to a RAID or RAID 5 >> setup? > > Depends on the controller I suppose. In the limited testing I have > done with my controller, there wasnt a hell of a lot of difference > between RAID0 and RAID 5. I'd guess that this was very limited testing--see above. Also, use rawio, not iozone or bonnie, for your testing. You can't generalize on performance. I have some stuff at http://www.lemis.com/vinum/, but it needs improvement. You may see a significant improvement over single disk configurations, even with RAID-5, depending on the layout. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message