Date: Sun, 1 Feb 1998 11:59:38 +1030 From: Greg Lehey <grog@lemis.com> To: Karl Denninger <karl@mcs.net> Cc: Jonathan Lemon <jlemon@americantv.com>, Brian Tao <taob@nbc.netcom.ca>, current@FreeBSD.ORG Subject: Re: RAID controllers - folks, check this thing out Message-ID: <19980201115938.38542@lemis.com> In-Reply-To: <19980131185203.60841@mcs.net>; from Karl Denninger on Sat, Jan 31, 1998 at 06:52:03PM -0600 References: <19980131144604.03410@mcs.net> <Pine.GSO.3.95.980131161942.27817Z-100000@tor-adm1> <19980131155527.19192@mcs.net> <19980131160423.30536@right.PCS> <19980131185203.60841@mcs.net>
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On Sat, Jan 31, 1998 at 06:52:03PM -0600, Karl Denninger wrote: > On Sat, Jan 31, 1998 at 04:04:24PM -0600, Jonathan Lemon wrote: >> On Jan 01, 1998 at 03:55:27PM -0600, Karl Denninger wrote: >>> RAID 5, due to the way it stripes parity across the volumes, has a "sweet >>> spot" in performance at 5 spindles. >> >> This is only true if your stripe set is 4 spindles. There's nothing >> wrong with using a stripe set of 8 spindles (9 devices), except that >> it tends to make small writes slower, since your data is spread out >> over more devices. >> >> 5 devices is not an inherent property of RAID 5, AFAIK. >> -- >> Jonathan > > The trade-off, however, between slowing down write performance, parity > computation, stripe size, etc seems to be right around 5 spindles. You can't say this without making assumptions about the nature of your access. What if it's 99.9% read access? What if it's 60% write access? Greg
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