Date: Tue, 4 Apr 1995 10:20:52 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: wilko@yedi.iaf.nl (Wilko Bulte) Cc: peter@bonkers.taronga.com, terry@cs.weber.edu, PVinci@ix.netcom.com, hackers@FreeBSD.org Subject: Re: large filesystems/multiple disks [RAID] Message-ID: <199504041720.KAA07847@gndrsh.aac.dev.com> In-Reply-To: <199504031905.VAA01885@yedi.iaf.nl> from "Wilko Bulte" at Apr 3, 95 09:05:08 pm
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> > > RAID does have the negative effect of of having to write 20% more data, > > thus cutting effective bandwidth by 20%. It is actually worse than > > this in that all writes must write to at least 2 drives no matter how > > small they are. The removes some of the benifits of stripping. > > And that is why some RAID systems use (battery backed up please ;-) RAM > caches. This works quite nicely. And you find these caches will fill up and some point in a sustained write test and you end up right back at the 20% performance loss I was talking about. Pure stripping of drives always outperforms RAID, you always pay some price for reliability, and it is usually performance or $$$. Humm.. wonder why no one is doing parrallel transfer SCSI drives, seems it would be easy to use 2 of the heads at once in a drive to effectivly double the drive electronics to media transfer rate. This could all be hidden in the drive electronics giving us disk drives that would be just as reliable and have 2x the transfer rate they currently do. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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