Date: Sun, 8 Nov 1998 06:30:17 -0500 (EST) From: Bill Vermillion <bill@bilver.magicnet.net> To: grog@lemis.com (Greg Lehey) Cc: freebsd-fs@FreeBSD.ORG Subject: Re: RAID1 Software vs Hardware Message-ID: <199811081130.GAA21734@bilver.magicnet.net> In-Reply-To: <19981108094916.T499@freebie.lemis.com> from Greg Lehey at "Nov 8, 98 09:49:16 am"
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Greg Lehey recently said: > 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: > >>>> 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? FreeBSD 2.5 versus SCO Opensever 5.0.4. I don't know whether it part of this can be contritubted to FreeBSD's synchronous writes, or whether it is all file system implementation dependant. The drive was on loan to a customer. They had a pair of old 4GB 'cuddas (slower than current drives), and lost a drive. I borrowed a 9GB 'cudda about 1230 AM and had them running. I used iozone the next week when the new 4GB returned. What surpsied me was that the older pair of 4GB in a RAID 0 were slower than the single 9GB - but only by about 200K/sec. The specs on the different models accounted for that. Individually the 2 older 4GBs were about 1/3 slower but were about the same in RAID 0. > > 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. A more correct choice of words should have been "raid-2/3/4" are commonly used. I seem to recall the spindle sync is not in the neweset 'cuddas and Cheetahs, while it was in the earilier 'cuddas. > >>> 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. ... You are speaking of 'ccd' when you make this statement? I trimmed previous posters quotes - and I believe the ccd comment came from you. I also think that is primitive. Doing that make the drive act like only a backup device. > 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). Yup. I can't see much use for a RAID in RAM. :-) Bill To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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