Date: Sun, 24 Jan 1999 11:49:05 -0600 (CST) From: "Jasper O'Malley" <jooji@webnology.com> To: Greg Lehey <grog@lemis.com> Cc: John Saunders <john.saunders@nlc.net.au>, freebsd-isp@FreeBSD.ORG Subject: Re: ccd and vinum Message-ID: <Pine.LNX.4.02.9901241128220.2571-100000@mercury.webnology.com> In-Reply-To: <19990124113845.L36690@freebie.lemis.com>
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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": * A volume is a logical disk. Client software, mainly file systems such as ufs and the virtual memory system, see it as a collection of bytes (character device) or sectors (block device). Unlike standard disk partitions, a Vinum volume is not subdivided into slices, since Vinum's mapping replaces disk slices. This can occasionally cause confusion to software such as newfs and fsck, which occasionally expect this structure. We'll look at this again later in the guide. For each Vinum volume, you must choose a name of up to 64 characters. It should adhere to normal UNIX device naming. As we will see below, you should avoid names ending in .p#, where # represents a digit. [snip] I'm a little confused about the terminology myself, Greg. Have you ever seen the AIX Logical Volume Manager? 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? For instance, the AIX LVM calls physical disk drives Physical Volumes (PV), which are grouped together in Volume Groups (VG). Each PV in a VG is divided into small disk partitions (default is 4MB per partition) called Physical Partitions (PP). 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. Mirroring is accomplished by assigning more that one PP to each LP in an LV. 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. 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). Is there a similar diagram you can draw for Vinum, Greg. I'd love to start using it myself :) Cheers, Mick The Reverend Jasper P. O'Malley dotdot:jooji@webnology.com Systems Administrator ringring:asktheadmiral Webnology, LLC woowoo:http://www.webnology.com/~jooji To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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