From owner-freebsd-fs Sat Nov 7 05:37:48 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id FAA03671 for freebsd-fs-outgoing; Sat, 7 Nov 1998 05:37:48 -0800 (PST) (envelope-from owner-freebsd-fs@FreeBSD.ORG) Received: from magicnet.magicnet.net (magicnet.magicnet.net [204.96.116.9]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id FAA03666 for ; Sat, 7 Nov 1998 05:37:47 -0800 (PST) (envelope-from bill@bilver.magicnet.net) Received: (from uucp@localhost) by magicnet.magicnet.net (8.8.6/8.8.8) with UUCP id IAA13694 for freebsd-fs@freebsd.org; Sat, 7 Nov 1998 08:35:36 -0500 (EST) Received: (from bill@localhost) by bilver.magicnet.net (8.9.1/8.9.1) id IAA10243 for freebsd-fs@freebsd.org; Sat, 7 Nov 1998 08:31:27 -0500 (EST) From: Bill Vermillion Message-Id: <199811071331.IAA10243@bilver.magicnet.net> Subject: Re: RAID1 Software vs Hardware In-Reply-To: <19981107200618.O499@freebie.lemis.com> from Greg Lehey at "Nov 7, 98 08:06:18 pm" To: freebsd-fs@FreeBSD.ORG Date: Sat, 7 Nov 1998 08:31:26 -0500 (EST) X-Mailer: ELM [version 2.4ME+ PL38 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org 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. 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. 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. I can't comment on IDE as I've never used them. > > 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. Bill To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message