[CentOS] Freeing pv space for snapshots
Jed Reynolds
lists at benrey.is-a-geek.net
Fri Jan 5 06:52:18 UTC 2007
Alvin Chang wrote:
> On 05/01/07, Aleksandar Milivojevic <alex at 8-p.ca> wrote:
>> I've used it, and it works correctly (and it is available in CentOS
>> 4.4). It shrinks file system as it should. The only things Paul should
>> be careful is to first shrink file system, than logical volume and to
>> correctly calculate file system size and by how many extents he can
>> shrink logical volume. If he shrinks logical volume too much, he might
>> end up loosing data. Running fsck in non-destructive mode (fsck -N)
>> and/or attempting to mount file system read-only after he shrinks
>> logical volume might be a good idea to test all is OK.
> A little technique you can use is:
> 1. shrink the file system to the size slightly less than what you
> really want
> 2. reduce LV to the size that is what you really want
> 3. expand the file system to the size of the LV (usually the resize
> program can be told to expand the file system to maximum available
> space automatically on the LV.)
>
That sounds like a pretty healthy tip!
Keep in mind that with a large LV, the slowest part of this process is
often the fsck -f step.
The resize2fs command is not nearly as slow as the fsck -f. But on a
large LV, you prolly want to show the progress bar during the resize, so
do a resize2fs -p, because I know I get nervous when I don't see output
from a long running command.
On production systems, I've learned to have enough space to have one
empty LV that can hold any of the other LVs so you can cleverly remount
a copy of the LV you want to either fsck or recreate. I don't want to
have a 2-hour reboot after 200 days uptime just to have my filesystem
force a fsck -f on you when you very like least want it. Recreating a LV
is a clever way to get around doing regular fscking, unless you tune
your filesystem check way out to 3 years and 999 reboots or whatnot.
Jed
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