Date: Mon, 25 Jan 1999 13:16:28 +1030 From: Greg Lehey <grog@lemis.com> To: "Jasper O'Malley" <jooji@webnology.com> Cc: John Saunders <john.saunders@nlc.net.au>, freebsd-isp@FreeBSD.ORG Subject: Re: ccd and vinum Message-ID: <19990125131628.C36690@freebie.lemis.com> In-Reply-To: <Pine.LNX.4.02.9901241128220.2571-100000@mercury.webnology.com>; from Jasper O'Malley on Sun, Jan 24, 1999 at 11:49:05AM -0600 References: <19990124113845.L36690@freebie.lemis.com> <Pine.LNX.4.02.9901241128220.2571-100000@mercury.webnology.com>
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On Sunday, 24 January 1999 at 11:49:05 -0600, Jasper O'Malley wrote: > On Sun, 24 Jan 1999, Greg Lehey wrote: > >> On Sunday, 24 January 1999 at 11:56:39 +1100, John Saunders wrote: > >>> way the documentation calls what I know as a partition, a subdisk. Also I >>> think the documentation has the slice and partition concepts swapped from >>> the way everything else on FreeBSD seems to work. For example "Unlike >>> standard disk partitions, a Vinum volume is not subdivided into slices," >>> But I thought is was the slices subdivided into partitions. i.e. wd0s1 >>> (i.e. slice 1) is disklabeled into partitions a b e f g. >> >> Where does this come from? It's not in the current documentation. > > It's on http://www.lemis.com/vinum.html, in the "Terminology" section, > under the definition for a Vinum "volume": > > <snip> Thanks. That's wrong, of course, and I've fixed it. In general, though, as the heading of this page says, This description is very preliminary information about Vinum. It contains significant errors, typos and omissions, but I don't have time to fix it now. When it is finished, I will replace this page with the ``final'' documentation. To this I have added: Please don't rely on it for technical details; the information in the man pages vinum(4) and vinum(8) is much more up to date. > I'm a little confused about the terminology myself, Greg. Have you ever > seen the AIX Logical Volume Manager? No. > It's probably the only thing I like about AIX :P If you have, could > you possibly relate the terminology used by the AIX LVM and Vinum? I'll try below. If anybody sees any obvious mistakes, tell me. I'm going only on your description. > For instance, the AIX LVM calls physical disk drives Physical Volumes > (PV), These would almost certainly be Vinum drives. > which are grouped together in Volume Groups (VG). Vinum doesn't have a similar concept. VERITAS does: it's purely a convenience, but in my experience it's an incovenience. > Each PV in a VG is divided into small disk partitions (default is > 4MB per partition) called Physical Partitions (PP). Oh. This sounds very restrictive. They'd correspond to Vinum subdisks, but subdisks can be any size. > These PPs can be combined from anywhere within the VG to form > Logical Volumes (LV). Once PPs are assigned to a LV, they > correspond to Logical Partitions (LP). > > In a standard configuration, there is a one-to-one mapping between a > PP and an LP. I think it might be possibly better to say that you combine PPs to make LPs, and LPs to make LVs. 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. > Mirroring is accomplished by assigning more that one PP to each LP in an > LV. I'm not sure this is stated correctly. I'd be more inclined to expect: ``Mirroring is accomplished by assigning more that one LP to an LV''. If that's the case, it would be directly translatable to Vinum terms: ``Mirroring is accomplished by assigning more that one plex to a volume''. > Logical volumes, then, correspond to traditional UNIX partitions (what we > call slices in FreeBSD). You can stick a filesystem on an LV, or swap > space, or a dump device, etc. > > It looks like this: > > VG -------- > | | > PV PV------- -------LV > | | | | > PP PP <--- 1-1, 2-1, 3-1 --> LP LP > > > The advantage to this, of course, is that you can grow filesystems by > tacking LPs onto an LV at any time. In Vinum, this depends on the organization. It works fine for concatenated plexes, but not (yet) for striped or RAID-5 plexes. In addition, we still haven't got round to telling UFS how to expand a file system. But it's all in the pipeline. > You can also use LVM tools to arrange which PPs are used by any > particular LV (e.g. so you can stick more frequently used data on > middle sectors of a physical volume). Right, same for Vinum. > Is there a similar diagram you can draw for Vinum, Greg. I'd love to start > using it myself :) > Drive Drive------- ---------Volume > | | | | > SD SD <--- 1-1, 2-1, 3-1 --> Plex Plex (SD stands for subdisk, of course). 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
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