Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!mcvax!ukc!pyrltd!bejc From: bejc@pyrltd.UUCP (Brian Clark) Newsgroups: comp.arch Subject: Re: Disk Striping (description and references) plus class brief Message-ID: <873@pyrltd.UUCP> Date: Wed, 5-Aug-87 04:03:47 EDT Article-I.D.: pyrltd.873 Posted: Wed Aug 5 04:03:47 1987 Date-Received: Sat, 8-Aug-87 08:58:13 EDT References: <2432@ames.arpa> Organization: Pyramid Technology Ltd, Camberley, Surrey, UK. +44 276 63474 Lines: 47 Summary: More information on disk striping In article <2432@ames.arpa>, eugene@pioneer.arpa (Eugene Miya N.) writes: > Very little work has been done on the subject yet a fair number of > companies have implemented it: Cray, CDC/ETA, the Japanese > manufacturers, Convex, and Pyramid (so I am informed), and I think > Tandem, etc. Now for important perspective: It seems that striping over > 3-4 disks like in a personal computer is a marginal proposition. > Striping over 40 disks, now there is some use. The break even-point is > probably between 8-16 disks (excepting the fault tolerance case). A > person I know at Amdahl boiled the problem down to 3600 RPM running on 60 > HZ wall clock: mechanical bottlenecks of getting data into and out of a > CPU from a disk. The work is not glamourous as making CPUs, yet is just > as difficult (consider the possibility of losing just one spindle). Pyramid has been shipping "striped disks" as part of OSx 4.0 since early this year."Striped disk" is one of 4 "virtual disk" types offered under OSx, the others being "Conatenated","Mirrored" and "Simple". A full description of the techniques and thier implementation were given by Tom Van Baak of Pyramid Technology Corporation at the February Usenix/Uniforum meeting in Washington. The principle reason for using "striped disk" is performance. The ability to place interleaved clusters of data on different spindles can be a winner in cases where the disk throughput rate is approaching the satuaration point of a single disk, and you have a disk controller intelligent enough to know where every disk head is at any given time. To take a case in point, ICC a company based in the City of London, supplies financial data from an 8Gbyte database to dial up subscribers. One index in the database is >800Mbyte long and has been set up on a "concatenated virtual disk" made up of two 415 Mbyte Eagles. When the set up was switched to the "striped virtual disk" model a throughput increase of 34% was measured. This doesn't mean that "striped" disks are going to answer everbody's disk performance problems, but they can provide significant improvements in certain cases. Both Tom and myself have produced papers on Virtual Disks and would be happy to answers any further questions that you have. Tom can be contacted at: pyramid!tvb while my address is given below. -- -m------- Brian E.J. Clark Phone : +44 276 63474 ---mmm----- Pyramid Technology Ltd Fax : +44 276 685189 -----mmmmm--- Telex : 859056 PYRUK G -------mmmmmmm- UUCP : !pyrltd!bejc