Date: Sat, 31 Jan 1998 18:54:54 -0600 From: Karl Denninger <karl@mcs.net> To: Brian Tao <taob@nbc.netcom.ca> Cc: current@FreeBSD.ORG Subject: Re: RAID controllers - folks, check this thing out Message-ID: <19980131185454.07579@mcs.net> In-Reply-To: <Pine.GSO.3.95.980131170825.27817a-100000@tor-adm1>; from Brian Tao on Sat, Jan 31, 1998 at 05:25:45PM -0500 References: <19980131155527.19192@mcs.net> <Pine.GSO.3.95.980131170825.27817a-100000@tor-adm1>
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On Sat, Jan 31, 1998 at 05:25:45PM -0500, Brian Tao wrote: > On Sat, 31 Jan 1998, Karl Denninger wrote: > > > > RAID 5, due to the way it stripes parity across the volumes, has a > > "sweet spot" in performance at 5 spindles. > > What "way" is that? On a given stripe, one drive provides the > parity block, the choice of drive staggered across consecutive > stripes. There may be an issue with small, sequential writes on a > RAID 5 set with a large number of drives, but I can't think of any > reason why five drives should be magical. > -- > Brian Tao (BT300, taob@netcom.ca) > "Though this be madness, yet there is method in't" A single write which does not consume an entire stripe requires that the entire stripe be READ FIRST in order to recompute parity. The more spindles involved in a stripe, the larger the write must be before this happens, and the worse the penalty if it does not. -- -- Karl Denninger (karl@MCS.Net)| MCSNet - Serving Chicagoland and Wisconsin http://www.mcs.net/ | T1's from $600 monthly to FULL DS-3 Service | NEW! K56Flex support on ALL modems Voice: [+1 312 803-MCS1 x219]| EXCLUSIVE NEW FEATURE ON ALL PERSONAL ACCOUNTS Fax: [+1 312 803-4929] | *SPAMBLOCK* Technology now included at no cost
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