From owner-freebsd-fs Sat Nov 7 15:19:55 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id PAA21326 for freebsd-fs-outgoing; Sat, 7 Nov 1998 15:19:55 -0800 (PST) (envelope-from owner-freebsd-fs@FreeBSD.ORG) Received: from allegro.lemis.com (allegro.lemis.com [192.109.197.134]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id PAA21319 for ; Sat, 7 Nov 1998 15:19:50 -0800 (PST) (envelope-from grog@freebie.lemis.com) Received: from freebie.lemis.com (freebie.lemis.com [192.109.197.137]) by allegro.lemis.com (8.9.1/8.9.0) with ESMTP id JAA04836; Sun, 8 Nov 1998 09:49:19 +1030 (CST) Received: (from grog@localhost) by freebie.lemis.com (8.9.1/8.9.0) id JAA02764; Sun, 8 Nov 1998 09:49:17 +1030 (CST) Message-ID: <19981108094916.T499@freebie.lemis.com> Date: Sun, 8 Nov 1998 09:49:16 +1030 From: Greg Lehey To: Bill Vermillion , freebsd-fs@FreeBSD.ORG Subject: Re: RAID1 Software vs Hardware References: <19981107200618.O499@freebie.lemis.com> <199811071331.IAA10243@bilver.magicnet.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.91.1i In-Reply-To: <199811071331.IAA10243@bilver.magicnet.net>; from Bill Vermillion on Sat, Nov 07, 1998 at 08:31:26AM -0500 WWW-Home-Page: http://www.lemis.com/~grog 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-fs@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Saturday, 7 November 1998 at 8:31:26 -0500, Bill Vermillion wrote: > Greg Lehey recently said: >> 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 >>>>> 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). ... > >>> 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. > > No - not theory. Measured in real-life - running HW raid 0 - on a > clients SCO system. We needed more speed. It may be slightly > under 50% - but it's darn close. Theory would tell you 50%. Practice shows it's darn close. If I had said "yes, that's what happens", somebody would have looked from the other perspective and said "not quite". > I have timed the same drive on SCO and FreeBSD - a 9GB 'cudda, and > the raw SCO performance through the file-system is in the 3MB/min > range, while using the FreeBSD file-system - as shipped - no mods, > etc,. it is between 2 and 3 times faster than SCO's. Which operating system? > Controller is DPT with a hunk of cache. All timing was done with > 100MB minimum file sizes usiing iozone. > >>> 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. > > I've only used HW RAID devices so I can't comment on the other > implementation. The RAID Standards Board (I think that's the > correct name) has permitted a pair of striped drives to be > designated RAID 0, while in reality it is not a RAID. > > They current have 6 classes - 0 thru 5 - and there is a chart > in Adaptec's book on I/O subsytems listing the pro's'/con's of > each. RAID2/3/4 aren't used, and from what I've seen drives that > use to have spindle sync for byte/sector striping aren't being made > anymore. But with drives now at 20MB/sec+ speeds, the old needs > are gone. Correct. You'd be surprised how many products offer RAID-2/3/4, though. I think the product manager got a checklist to tick off. I have deliberately left these three out of Vinum. > I can't comment on IDE as I've never used them. Shouldn't make much difference with only one drive per controller and UDMA. Otherwise you'll run into significant contention problems. >>> 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. > > Reading from two disks for different files is one of the touted > features of most HW implementations. Put it this way, I don't know of any other implementation, SW or HW, which is this primitive. Vinum has a choice of round robin (default) or always reading from a specific drive (which can be an advantage if you have a ramdisk, for example). 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