Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!ucbvax!PAN.SSEC.HONEYWELL.COM!thompson From: thompson@PAN.SSEC.HONEYWELL.COM (John Thompson) Newsgroups: comp.sys.apollo Subject: re: Stripe Disk on DN10000 Message-ID: <9009210317.AA14796@pan.ssec.honeywell.com> Date: 21 Sep 90 03:17:04 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 60 > We are about to stripe two 700 MB disk (with separate > disk controller) together. However, we are not sure that the following > procedures as defined in /usr/man/cat8/invol.8 is correct, and no one > else in local Apollo Support Group can help us with this as they have > never done this before. We would appreciate any comments. > ... > The excised text seems correct -- it appears that you did the right thing, or that the example (if that's what it is) is correct. Here's the scoop, from someone who has striped disks many ways, many times -- Executing INVOL option '1 -m' does no formatting. What it _DOES_ do is set up some internal junk (with the Phys Volume label?) so that the node refers to ALL drives when you mention the primary. After you tell it what drive to format (e.g. w0:0) it'll ask how you want them striped, and how many drives you're striping together. After you feed it all the info, it does virtually nothing (for maybe 15 seconds?) and then tells you to execute option 2. Option 2 is normally used to add logical volumes to a single disk. However, now that there's disk striping, it really adds logical volumes to a single VIRTUAL disk (which is one or more PHYSICAL drives). The newly striped disk (I'll refer to each physical disk as a 'drive') has a huge vacancy -- the entire media is empty! Now you specify the volumes that will be on this disk (if you don't stripe, INVOL option 1 asks you this stuff), and how rigorously you want to format (no verification, format/write, format/write/read). Notice that, once you stripe drives into a disk, the multi-disk set is referred to by its primary number -- the first drive that you mentioned when you ran INVOL option 1. This referencing goes for INVOL, SALVOL, MTVOL, the Unix mount commands, .... There are 2 methods of striping disks -- 'cylinder' and 'sector'. If you have 1 controller per drive, sector striping will speed up disk access. If you have multiple drives per controller, sector striping will slow down access. The reason is fairly simple -- in sector striping, each drives cylinders are logically combined, with one drive having the even sectors and one having the odd (I'm assuming 2 drives). If you have 2 controllers, each one can ask for a sector, and you get back 2 sectors in about the same time you get one. If you have 1 controller and 2 drives, you get no possibility of parallel accesses (the controller waits for the drive to respond), and you get no possibility of multiple sectors being returned from a single disk access. You need to ask for drive 0's info, drive 1's, drive 0's, drive 1's, etc. With cylinder striping, you get no speedup/degredation regardless. In this case, one drive gets the even CYLINDERS, and the other gets the odd ones. Even with two controllers, you'll rarely need information that happens to be at the tail of one drive's cylinder and the head of the other drive's next cylinder. Be warned that, when you stripe drives, you're putting data on a disk that's twice as likely to fail. If either drive bites it, the entire multi-disk needs to be formatted. On the other hand, you can get higher throughput, larger capacity, more impressive 'lvolfs / df' responses, .... :-) Good Luck -- hope this helps. John Thompson (jt) Honeywell, SSEC Plymouth, MN 55441 thompson@pan.ssec.honeywell.com As ever, my opinions do not necessarily agree with Honeywell's or reality's. (Honeywell's do not necessarily agree with mine or reality's, either)