Date: Sat, 7 Nov 1998 08:31:26 -0500 (EST) From: Bill Vermillion <bill@bilver.magicnet.net> To: freebsd-fs@FreeBSD.ORG Subject: Re: RAID1 Software vs Hardware Message-ID: <199811071331.IAA10243@bilver.magicnet.net> In-Reply-To: <19981107200618.O499@freebie.lemis.com> from Greg Lehey at "Nov 7, 98 08:06:18 pm"
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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 > >>> <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). ... > > 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
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