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List:       evms-devel
Subject:    [Evms-devel] Moving parts of filesystems
From:       Ross Boylan <RossBoylan () stanfordalumni ! org>
Date:       2004-05-28 15:37:49
Message-ID: 20040528153749.GO2067 () wheat ! boylan ! org
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With a bigger disk I have the opportunity to straighten out my
filesystem.  There are a couple of operations I want to do involving
moving the contents of part of a file system.

I could probably get away with just cp -a or tarring the relevant
parts, but there is some chance this would lose some updates.  evms
has a number of facilities that seem close to what I need, but I can't
quite see how they would work.  I think these kinds of operations are
not evms's specialty, but I thought I'd check here to see if anyone
had any suggestions.

Big Picture, the options I see are
1) do a cp or tar online and hope
2) do 1) after going into single user mode, which will reduce the
chance of problems
3) create and boot into a new copy of the OS and manipulate from there
(completely safe, but awkward).
4) use evms (either replace or snapshot seems most likely to help).

There are two scenarios:

I) /var/spool/news is symlinked to /usr/local/var/spool/news.
I want to put the contents of the latter back on my already moved /var
volume.

II) Migrate my old /usr/local hierarchy to a new /usr/local.
/usr/local is itself only part of the /usr volume, and it includes
several subdirectories that are mounted from /evms/scratch via bind:
$ mount  # relevant part of output only shown
/dev/ide/host0/bus0/target0/lun0/part6 on /usr type ext2 (rw)
/dev/evms/scratch on /evms/scratch type reiserfs (rw)
/evms/scratch/apt-cache on /usr/var/cache/apt type none (rw,bind)
/evms/scratch/local/download on /usr/local/download type none (rw,bind)
/evms/scratch/kde3 on /usr/local/src/kde3 type none (rw,bind)

In terms of using evms, here's my thinking.

replace isn't quite right because I am carving up and recombining
volumes.

snapshot isn't quite right because it captures the state of the volume
at some past time, whereas I want something that is current.  Also, it
is oriented to volumes, not directory hierarchies.

mirroring might help some of the move, but is again limited to
volumes.  Also, having followed another thread on mirroring, I'm a
little unsure how to do it.  As I understand it, mirroring can not be
added after the fact to a volume, even evms native ones.  So it
perhaps requires a two step procedure of creating a mirror storage
object and then using it to replace the original.  Unfortunately,
replace is not an option for /usr, since it is not on an evms native
volume.

I should also mention that I'm trying to keep / and /usr off of evms
to simplify my system start up and disaster recovery.  I have plenty
of free space to play with.

The short version of this is that I think I need to create another OS
and manipulate my partitions and directories from there, but I'd love
to hear otherwise.

Thanks.

P.S. If I make a new OS partition, I'm thinking of using a Linux 2.6
kernel, vs the 2.4 one I use now.  Am I going to run into any problems
mixing the two flavors of evms's?  Specifically, I would create
volumes under 2.4, then use 2.6 to copy files around (and perhaps
manipulate the volumes further), then boot back into 2.4 to access the
new volumes.



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