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SubjectRe: Volume Managers in Linux
Let me first appologize.  It sounds like I bash MD as bad code; I
just think there's better ways to go about what MD does.

On Mon, 2 Nov 1998, MOLNAR Ingo wrote:
> in what way isnt MD clean ... ? And in what way is LVM standard? Can you

First, I would like to say MD is all well and good, and if you ask,
"Why is MD not clean?", it is really two questions...
1) Is MD the *clean* way to do what MD does?
2) Is MD cleanly implemented.

I guess I think it fails test #1, but passes #2. I don't think
this sort of messiness really belongs wholely in the kern. I like
the idea of having the virtualization of an LV in kernel. It allows
userland to do it's thing.

Kind of like KGI/GGI. Uhh... Don't mean to start another holy war...

> show me some documentation/standard that specifies how LVM should look
> like, apart from vague assertions like "uhm, something like Veritas or
> AIX's stuff, or maybe HP's?".
> -- mingo

A layer that provides a virtual view of physical disk. One that
has VGs [Groups of physical volumes (disks or partitions)], PEs [Extents
of said VGs in tunable sizes], and LVs [Logical Volumes] which are made
from PEs.

A volume group can have alocation policies [strictly contiguous, whatever]
so you can control just how your disk pool, or, VG will allow use.
Because LVM is basically at it's core a physical -> logical address
remapping mechanism, RAID, mirroring, and all the goodies fit REAL
nice in userland.

Wouldn't you like to push all that crap out to userspace?

Both Sun and HP use Veritas's LVM.
(http://www.veritas.com/product-info/vm/index.htm)

Heinz's LVM is concepually like it, I think.
(http://linux.msede.com/lvm/slides.html)

-Shawn
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