Re: Convert ext4 lvm to normal ext4 partition

On 12/11/10 2:04 PM, Michael Miles wrote:
Patrick O'Callaghan wrote:
On 12/11/10 1:13 PM, Michael Miles wrote:
Considering that the LVM is a ext4 Virtual partition it seems to me
that it would be easy to convert but there is no such beast out there
Lots of stuff for converting ext3 to ext4 but nothing for what I need.

This is pure speculation on my part, but I'm guessing one reason it's
hard is that the LVM layer knows nothing about the ext4 layer. The
ext4 layer contains lots of metadata (inodes, freelists, etc.) which
includes pointers to disk sectors or extents. In a physical partition
these point to real disk addresses but in an LVM partition they are
virtual (compare real with virtual memory for an analogy). From LVM's
viewpoint the entire ext4 fs is just disk sectors with random binary
data. The fact that some of this stuff is fs metadata and some isn't
means that a conversion tool would need to understand the ext4
metadata to convert it. Of course if it's ext3 or xfs or btrfs etc.
then the same applies, with different rules for each one.

Worse still, if you want a in-place conversion you have to be able to
do this in such a way that it's recoverable even after a hard system
crash in the middle of the conversion. And if you don't need it
in-place, you already have the solution as said before.

Just my 2 cents.

poc
Agreed, I am just really surprised that Fedora would adopt this method
of storage as it slows down the drive by a huge margin.
That reason alone would say to me' No, don't want this"

Perhaps there are other benchmarks with different results, I don't know.
In any case, Fedora presumably decided that the gain in flexibility was
worth it. The irony is that there *is* a considerable gain for people
with large systems, server farms, clusters and what have you. For the
ordinary desktop user it's much more open to question, particularly as
some tools (notably parted) don't support it. Case in point: my F13 LVM
layout suffered a number of changes during its life, basically because I
needed to expand / at the expense of /home. The upshot was that the LV
containg / was physically (but not logically) split in two
non-contiguous regions. Then I decided to expand the /boot partition,
which of course is not in LVM. This meant resizing /, freeing space at
the end of the disk and moving the physical partition where LVM lived,
but of course parted refused since it doesn't understand LVM.

I consulted Google, and this list, and a very knowledgeable friend, and
the LVM docs, and concluded that there was no avoiding messing with the
disk partition table via fdisk. Needless to say I lost everything.
Luckily I have a nightly backup to a NAS so the day was saved, and I
then got to do a completely clean install of F14. So maybe LVM is a Good
Thing after all :-)

poc
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Relevant Pages

  • Re: Convert ext4 lvm to normal ext4 partition
    ... Lots of stuff for converting ext3 to ext4 but nothing for what I need.. ... hard is that the LVM layer knows nothing about the ext4 layer. ... these point to real disk addresses but in an LVM partition they are ... if you want a in-place conversion you have to be able to ...
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  • Re: Convert ext4 lvm to normal ext4 partition
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