Date: Tue, 04 Apr 1995 14:40:04 -0700 From: "Justin T. Gibbs" <gibbs@estienne.CS.Berkeley.EDU> To: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> Cc: wilko@yedi.iaf.nl (Wilko Bulte), peter@bonkers.taronga.com, terry@cs.weber.edu, PVinci@ix.netcom.com, hackers@FreeBSD.org Subject: Re: large filesystems/multiple disks [RAID] Message-ID: <199504042140.OAA12675@estienne.cs.berkeley.edu> In-Reply-To: Your message of "Tue, 04 Apr 1995 10:20:52 PDT." <199504041720.KAA07847@gndrsh.aac.dev.com>
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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. Is this still true with hardware parity calculation? >Pure stripping of drives always outperforms RAID, you always pay some >price for reliability, and it is usually performance or $$$. > ... >-- >Rod Grimes rgrimes@gndrsh.aac.dev.com >Accurate Automation Company Custom computers for FreeBSD -- Justin T. Gibbs ============================================== TCS Instructional Group - Programmer/Analyst 1 Cory | Po | Danube | Volga | Parker | Torus ==============================================
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