Date: Tue, 7 Mar 2000 18:20:29 +1100 From: Greg Lehey <grog@lemis.com> To: Mike Tancsa <mike@sentex.net> Cc: James <mlistbsd@icorp.net>, questions@FreeBSD.ORG Subject: Re: RAID/config questions Message-ID: <20000307182029.C331@mojave.worldwide.lemis.com> In-Reply-To: <38c48132.1056418179@mail.sentex.net>; from mike@sentex.net on Tue, Mar 07, 2000 at 04:15:35AM %2B0000 References: <MAIL38C45697.D736070F@icorp.net> <38c48132.1056418179@mail.sentex.net>
next in thread | previous in thread | raw e-mail | index | archive | help
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 I don't know which one to recommend, but the supported DPT boards are rather out of date.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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20000307182029.C331>