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Re: [linux-lvm] LVM onFly features





--On December 10, 2005 9:06:46 PM +0100 Marc-Jano Knopp <pub_ml_lvm marc-jano de> wrote:

On Sat, 10 Dec 2005 at 13:03 (-0700), Michael Loftis wrote:
--On December 10, 2005 8:48:27 PM +0100 Marc-Jano Knopp
<pub_ml_lvm marc-jano de> wrote:
> On Sat, 10 Dec 2005 at 14:38 (-0500), Mag Gam wrote:
>> any news about hot(no unmount, no fsck, no fs resize) ext2/ext3
>> filesystem increase?
>
> And when will online-*shrinking* of ext3 appear?

These are not LVM features.  These are filesystem features.  Better to
ask  on lkml, or the maintainers directly.

D'oh! Sorry for that, I was misguided by the previous post!

Not a problem, a lot of people don't see the delineation right off. Filesystems like VXVFS (Veritas) in their commercial implementations are really LVM+Filesystem in one. Not sure what the linux port is looking like these days though.

ReiserFS has hot expansion capabilities, but no (yet?) hot shrinking capabilities. One of the reasons it has these features and ext2/3 does not is because ext2/3 are very old filesystems designed on a different mentality of a static filesystem. On-line expansion of ext2 based filesystems is an extremely complicated venture, it might honestly even be impossible.

ReiserFS has the advantage here because it doesn't necessarily pre-write out a lot of filesystem meta-information (superblocks, inodes, bitmaps, etc), instead these structures are entirely dynamic to begin with, so enlarging them at runtime is trivial, requires a very short lock and a change to a few numbers. Ext2 resizing requires actually rewriting a lot of filesystem metadata.


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