Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!cmcl2!rutgers!topaz.rutgers.edu!ron From: ron@topaz.rutgers.edu (Ron Natalie) Newsgroups: comp.unix.wizards Subject: Re: Disk striping? (4.3 BSD) Message-ID: <16829@topaz.rutgers.edu> Date: Fri, 4-Dec-87 12:22:38 EST Article-I.D.: topaz.16829 Posted: Fri Dec 4 12:22:38 1987 Date-Received: Wed, 9-Dec-87 04:44:47 EST References: <2369@emory.uucp> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 38 First, striping is not defined precisely as you indicate. There are several ways one might use multiple drives on a UNIX system. 1. First method (currently in use). Chop your filesystem into part and place them on separate drives. Provided you have a controller that allows you to do overlapped seeks you can arrange for better access times by care placement of filesystems. Note that / and /tmp are the heaviest usage filesystems on most systems. If you have multiple controllers, then you can actually do two transfers at a time, providing for better througput. 2. Second method, span file system accross multiple physical devices. This was done in some Unixes, especially on disk drives like RS04's whose size is prohibitedly small. Of course, this isn't that hot of an idea as it guarantees that only one drive will be active at a time. 3. Stripe the drives. Interleave the filesystems between two drives so that you can transfer data requests from both drives at once. This only beats out method #1 if you have the following: 1. A controller capabale of transferring to/from each drive simoultaneously (or doing the same with multiple controllers). 2. A controller with "zero latency" feature. Most controllers even when the I/O is a full track (or a sustantial fraction of it) wait until the beginning of the track comes under the head before starting the transfer. Using these controllers causes you to head towards the maximum latency as you must wait for the maximum latency on each drives which will be statistically higher than the single drive feature. Newer controllers will start transferring as soon as they realize that there is valid data under the head that is part of the request. -Ron