Date: Tue, 3 Aug 1999 23:20:45 +0200 From: Bernd Walter <ticso@cicely.de> To: Greg Lehey <grog@lemis.com> Cc: Bernd Walter <ticso@cicely.de>, Stephen Hocking-Senior Programmer PGS Tensor Perth <shocking@prth.pgs.com>, hackers@FreeBSD.ORG Subject: Re: Adding disks -the pain. Also vinum Message-ID: <19990803232044.A25368@cicely8.cicely.de> In-Reply-To: <19990803155945.W62948@freebie.lemis.com>; from Greg Lehey on Tue, Aug 03, 1999 at 03:59:46PM %2B0930 References: <19990803133554.S62948@freebie.lemis.com> <199908030416.MAA16945@ariadne.tensor.pgs.com> <19990803081216.B23148@cicely8.cicely.de> <19990803155945.W62948@freebie.lemis.com>
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On Tue, Aug 03, 1999 at 03:59:46PM +0930, Greg Lehey wrote: > On Tuesday, 3 August 1999 at 8:12:17 +0200, Bernd Walter wrote: > > > For UFS/FFS there is nothing worth seting the stripesize to low. > > It is generally slower to acces 32k on different HDDs than to acces 64k on > > one HDD. > > It is always slower where the positioning time is greater than the > transfer time for 32 kB. On modern disks, 32 kB transfer in about 300 > µs. The average rotational latency of a disk running at 10,800 rpm is > 2.8 ms, and even with spindle synchronization there's no way to avoid > rotational latency under these circumstances. It shouldn't be the latency, because with spindlesync they are the same on both disks if the transfer is requested exactly the same time what is of course idealized.. The point is that you have more then a single transfer. With small transfers spindle sync is able to winback some of the performance you have lost with a to small stripe size. > > > Spindle Sycronisation won't bring you that much on modern HDDs - I tried > > it using 5 Seagate Elite 2.9G (5,25" Full-Height). > > It should be useful for RAID-3 and streaming video. I case of large transfers it will make sense - but FFS is unable to set up big enough requests. -- B.Walter COSMO-Project http://www.cosmo-project.de ticso@cicely.de Usergroup info@cosmo-project.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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