Date: Sat, 7 Nov 1998 20:06:18 +1030 From: Greg Lehey <grog@lemis.com> To: Bill Vermillion <bill@bilver.magicnet.net>, freebsd-fs@FreeBSD.ORG Subject: Re: RAID1 Software vs Hardware Message-ID: <19981107200618.O499@freebie.lemis.com> In-Reply-To: <199811070042.TAA27229@bilver.magicnet.net>; from Bill Vermillion on Fri, Nov 06, 1998 at 07:42:15PM -0500 References: <Pine.BSF.4.05.9811061332290.455-100000@ender.sf.scient.com> <199811070042.TAA27229@bilver.magicnet.net>
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On Friday, 6 November 1998 at 19:42:15 -0500, Bill Vermillion wrote: > Christopher Nielsen recently said: > >> On Fri, 6 Nov 1998, Bagnara Stefano wrote: > >>> Date: Fri, 6 Nov 1998 17:35:58 +0100 From: Bagnara Stefano >>> <bago@datasail.it> To: freebsd-fs@FreeBSD.ORG Subject: RAID1 >>> Software vs Hardware ^^^^^ > >>> I need to implement a simple raid1 with 2 9gigs SCSI HDD. I . >>> Ineed a inexpensive solution ... so i was thinking about a . >>> Isoftware raid1 s it possible? is it too slow? the system will . >>> Ibe only a mail server . > >> Your really not going to see very good performance with RAID if >> you're using only two spindles (i.e., discs). You might want >> to try going with 4 4G discs, if possible. The question of >> performance is directly related to exactly how much I/O you're >> going to be shoving through the discs. "Only a mail server" >> doesn't really provide enough information, IMHO. > > I've found that I get a 50% throughput increase (typical)when > running RAID 0 with 2 drives. That's what theory would tell you. > RAID 0 is always the fastest, but any failure will stop you dead. (if that's all you do). > RAID 1 will give no increase in some areas, and writes are slower, This depends a lot on the configuration. You need to write to every copy (plex in vinum jargon), whereas you only need to read from one. In practice, if you're running SCSI disks or IDEs with UDMA on different controllers, you'll delay the writes to the speed of the slowest disk. On average that's slower than a single disk, but not much. > but it will boost the read throughput if different files are being > accessed, just as if you load balanced multiple single disks.. BTW, ccd always reads from the same copy of the data, so this doesn't work. But in principle you're right. > A good bet is a small boot drive, and then put the stripes on a > pair of larger drives. Thus you have the recovery tools in place > to restore after a disaster. Otherwise you have to go back > to square one and install the OS. Not a big problem in a 2 drive > mirror - but still a safety factor. Agreed Greg -- See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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