From owner-freebsd-isp Mon Jan 25 17:58:02 1999 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id RAA26301 for freebsd-isp-outgoing; Mon, 25 Jan 1999 17:58:02 -0800 (PST) (envelope-from owner-freebsd-isp@FreeBSD.ORG) Received: from allegro.lemis.com (allegro.lemis.com [192.109.197.134]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id RAA26263 for ; Mon, 25 Jan 1999 17:57:58 -0800 (PST) (envelope-from grog@freebie.lemis.com) Received: from freebie.lemis.com (freebie.lemis.com [192.109.197.137]) by allegro.lemis.com (8.9.1/8.9.0) with ESMTP id MAA03157; Tue, 26 Jan 1999 12:27:55 +1030 (CST) Received: (from grog@localhost) by freebie.lemis.com (8.9.2/8.9.0) id MAA68254; Tue, 26 Jan 1999 12:27:54 +1030 (CST) Date: Tue, 26 Jan 1999 12:27:53 +1030 From: Greg Lehey To: "Jasper O'Malley" Cc: John Saunders , freebsd-isp@FreeBSD.ORG Subject: Re: ccd and vinum Message-ID: <19990126122753.B66239@freebie.lemis.com> References: <19990125131628.C36690@freebie.lemis.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.95.1i In-Reply-To: ; from Jasper O'Malley on Mon, Jan 25, 1999 at 08:56:35AM -0600 WWW-Home-Page: http://www.lemis.com/~grog Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-41-739-7062 Sender: owner-freebsd-isp@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Monday, 25 January 1999 at 8:56:35 -0600, Jasper O'Malley wrote: > On Mon, 25 Jan 1999, Greg Lehey wrote: > >> I think it might be possibly better to say that you combine PPs to >> make LPs, and LPs to make LVs. > > Sort of, but not quite. LVs are made up of LPs. But exactly how many PPs > are in each LP of a particular LV depends on the "mirror" property of an > LV. If it's not mirrored, there is exactly one PP per LP. If it's a > simple mirror, there are exactly two PPs for each LP in the LV. If it's a > double mirror, there are exactly three PPs for each LP in the LV. Each LP > in a particular LV has the same number of PPs as every other LP in that > LV. That's where the jump from "physical" to "logical" is made. Ah. What you're saying is that each LP also has the same storage size as a PP (4 MB), and that you're combining a number of them to make up the size of the LV? >> In this case, a PP corresponds to a subdisk (but it's less >> flexible), an LP corresponds to a plex, and an LV corresponds to a >> volume. > > I think I'm beginning to see the difference...in the LVM, PPs are used are > used as simple building blocks, all of a uniform size. I can make a LV of > any size I want (as long as it's a multiple of the PP size) by picking off > PPs from anywhere within the VG. That's also how I can grow the > filesystem, by simply adding more PPs (via LPs) to the LV. > > The only thing that's got me confused about Vinum is whether or not a plex > has to exist within a single subdisk, or whether it can span subdisks, OK. We're looking at this from a different side. If I've understood you correctly, a 16 MB mirrored LV would look like: ------------------------- | | | | PP0 | PP1 | LP 0 (0-3 MB) | | | ------------------------ | | | | PP2 | PP3 | LP 1 (4-7 MB) | | | ------------------------ | | | | PP4 | PP5 | LP 2 (8-11 MB) | | | ------------------------ | | | | PP6 | PP7 | LP 3 (12-16 MB) | | | ------------------------ In Vinum, a 16 MB mirrored volume made of 4 MB subdisks might look like this: Plex 0 Plex 1 ------------------------- | | | | SD0 | SD1 | (0-3 MB) | | | ------------|----------- | | | | SD2 | SD3 | (4-7 MB) | | | ------------|----------- | | | | SD4 | SD5 | (8-11 MB) | | | ------------|----------- | | | | SD6 | SD7 | (12-16 MB) | | | ------------------------ The result is the same, but the concept of plexes is pretty much the opposite of the concept of LPs. In particular, I don't see how you can stripe effectively with the LVM approach. This diagram should also answer your question above: plexes contain one or more subdisks. > and whether or not two plexes of a particular volume must take up > the same number of subdisks (or have roughly the same subdisk > layout, at least). No. There's no constraint there. Greg -- See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message