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
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С тем, что не помешает никогда,
Kittle