[linux-lvm] Total free space using added VGs and LVs

Ryan Anderson ryan at worldspice.net
Fri Oct 23 20:12:51 UTC 2009

Your best bet for resizing the root FS will be to use a LiveCD with LVM2
support. sysrescuecd works well, but likely your distribution install
disk can be booted with "linux rescue" or something similar.

Lou Arnold wrote:
> Luca, your comments make sense. After my last message I considered just
> what you said, but I don't know how to prove it.
>> I know there is no data on the drive that I added, because I just added
> the drive and never put data on it. I am sure "busy" means that it is
> mounted.�Because it is�included in the default group/volume (VolGroup00
> - LogVol00) and because that LV is mounted at root ("/"), I cannot
> reduce the filesystem with resize2fs; there is no way to unmount "/",
> that I know of, anyway.�� Unless of course someone knows how?
> On Thu, Oct 22, 2009 at 11:52 PM, Luca Berra <bluca at comedia.it
> <mailto:bluca at comedia.it>> wrote:
>     On Wed, Oct 21, 2009 at 03:03:24PM -0400, Lou Arnold wrote:
>         I read the How-To. It doesn't talk about the specific case or
>         being mounted
>     I hate how-tos, they are a collection of particular cases and leave the
>     luser with a feeling of knowledge. which is not.
>         at root, so I had to experiment. It is likely that commands were
>         in the
>         wrong order, but I don't know what the right order is.
>         I have attached the terminal session I used. In the end it did
>         not work.
>     the commands were not in the wrong order,
>     they were just the wrong commands, unless your aim was reinstalling.
>         There was still 66 GB free, and when I rebooted, the file system
>         failed. The
>         superblock was too big.
>         I obviously don't understand the difference between pvresize,
>         lvreduce and
>         vgreduce, and how �resize2fs �is related to these commands.
>     I think you need to go over the basics again
>     LVM is used to abstract storage management
>     it is done by creating layers
>     Physical Volumes: which represent disks (or partitions, or whatever
>     block device...)
>     Volume Group: which is a collection of disks
>     Logical Volume: which is a portion of a volume group
>     LVM allows to add/remove PVs to/from a VG. Add/remove/increase/shrink
>     LVs in a VG.
>     This is done by dividing each PV in Physical Extents (PE), and then
>     mapping those to Logical Extenst (LE) in a LV, so a LV is composed of
>     chunks of disk taken from one or more PV in a VG.
>     When using lvm you create filesystems over logical volumes instead of
>     creating them on disk (or partition....)
>     Lvm has no knowledge of what lays over it, a logical volume
>     is just a block device.
>     The above sentence means that if you use a logical volume to host a
>     filesystem and want to resize the lv, you have to deal with the
>     filesystem yourself.
>     i.e.
>     if you enlarge a LV, you have to tell the filesystem that the space
>     available has increased.
>     if you want to reduce an LV, you have to ensure _before_ doing it that
>     the space removed does not contain any data.
>     so if you want to reduce an LV containing a filesystem you _have_ to
>     tell the filesystem _before_ to let that space alone. if you fail to do
>     this you will loose all data that was on the portion of disk you
>     removed, and the filesystem will still think it can use that portion of
>     data, until it will actually try, then sudden realization will hit like
>     a brick. as you just discovered.
>     btw, let pvresize alone, it is used only in the particular case in which
>     you are able to resize the disk underlying a volume group, which is
>     impossible for a plain disk.
>     L.
>     _______________________________________________
>     linux-lvm mailing list
>     linux-lvm at redhat.com <mailto:linux-lvm at redhat.com>
>     https://www.redhat.com/mailman/listinfo/linux-lvm
>     read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> ------------------------------------------------------------------------
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Ryan Anderson
(901) 843 9300
Systems Engineer
WorldSpice Technologies

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