Date: Thu, 19 Feb 1998 19:14:52 +0100 (MET) From: Wilko Bulte <wilko@yedi.iaf.nl> To: shimon@simon-shapiro.org Cc: freebsd-scsi@FreeBSD.ORG, curt@kcwc.com Subject: Re: getting oriented with RAID Message-ID: <199802191814.TAA01167@yedi.iaf.nl> In-Reply-To: <XFMail.980218113023.shimon@simon-shapiro.org> from Simon Shapiro at "Feb 18, 98 11:30:23 am"
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As Simon Shapiro wrote... > > On 18-Feb-98 Wilko Bulte wrote: > > ... > > > You want to stay on the outside of your ZBR platters to achieve the > > highest datarates. > > My age is showing ... :-) Yes, on modern disks, the number of sectors per > platter varies, decreasing towards the spindle. Ach. Ultrix-11 on PDP11/34 with 2x RK05, now that's ancient ;-) > >> all this nonsense), just experiment with drives, busses, stripe sizes, > >> amount of cache, cache utilization, host cache vs. DPT cache, etc. > > > > Not to forget write-back caching (with battery backup please) > > Of course. Caching policy has a huge performace impact. but you know, at > a certain point it all dies anyway. Consider a recent project with over 1 > billion records in the database. Cache hit rate is nil, either way. the > only thing that helps there is elevator sorts and deep execution queues. For single stream reads etc cache is pretty useless. But you want WB cache anyway to avoid RAID5 writehole pittfalls. So, e.g. data has been updated on disk but the corresponding parity block never made it to disk when the power went out. W/ _ ______________________________________________________________________ | / o / / _ Bulte email: wilko @ yedi.iaf.nl http://www.tcja.nl/~wilko |/|/ / / /( (_) Arnhem, The Netherlands - Do, or do not. There is no 'try' --------------- Support your local daemons: run [Free,Net,Open]BSD Unix -- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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