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SubjectRe: Volume Managers in Linux
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In message <19981103181157.A17442@enchanted.net>, Aaron Wrasman writes:
+-----
| The filesystem has nothing to do with it. All LV gives you on AIX is a way to
| lay things out on multiple physical disks. LVs are just part of a volume grou
+--->8

The AIX JFS has a *lot* to do with it, because you can resize (well, expand)
JFS filesystems from LVM and JFS will immediately make use of the space.
This implies that JFS handles its own allocations in such a way that it can
integrate new logical extents into itself "on the fly". And I *do* mean "on
the fly" --- you don't have to unmount/take the filesystem offline before
extending it, a fact which was very useful when I had to increase the size
of / on several CEDA machines recently. JFS picked up on the added space
immediately.

In short, AIX LVM works well because JFS is tightly integrated with it.

Certainly you can manipulate non-JFS partitions with LVM and it will "work"
--- but e.g. Oracle will never make use of additional extents you add to one
of its volumes. Nor will its own internal space allocation be aware of how
the LVM is reorganizing, duplicating, etc. its data. Neither would a
hypothetical ext2fs implementation for AIX, unless it were redesigned to
work with LVM (and it would not work well without a significant redesign, I
suspect).

This is why we need better communication between any LVM layer and the next
layer up. (Imagine Oracle for Linux knowing how to work with an LVM. I'm
pretty sure Oracle for AIX doesn't, but Oracle would have (a) the LVM source
and (b) the ability to work with us to insure the LVM design would fit well
with Oracle's raw volume management.)

--
brandon s. allbery [os/2][linux][solaris][japh] allbery@kf8nh.apk.net
system administrator [WAY too many hats] allbery@ece.cmu.edu
carnegie mellon / electrical and computer engineering KF8NH
Kiss my bits, Billy-boy.



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