[gentoo-user] LVM: extending volume groups and logical volumes

[Allan Gottlieb]

I need to add space to /var (thank you, libreoffice), which is on lvm.
Since my one volume group vg is getting low, I thought this would be a
good time to extend it as well.

Alan (McKinnon) has posted very helpful lvm bits (reprinted below).
Following alan's bottom up creation mandate I believe the idea is

phy disk:   /dev/sda  my only drive
phy part:   fdisk   create another partition of type LVM (/dev/sda8)
phy vol:    pvcreate /dev/sda8
vol grp:    vgextend vg /dev/sda8
log vol:    lvextend --size +10G /dev/vg/var
file sys:   resize2fs /dev/vg/var
files/dirs: not relevant

Questions

1.  Apparently 2.6 (hence 3.x) kernels can expand mounted file systems
    (/var is mounted as ext3).

    Since I can't unmount /var because it is in use, I guess that, if I
    every need to shrink /var, I would need to boot off a CD.  Is that
    correct?

    Back in the day, we had single user mode for this, but I don't see
    how to get the equivalent now.

    Is it really safe to extend /var (i.e., /dev/vg/var) while mounted
    as ext3?  It sounds frightening since daemons could start running
    and access /var.

2.  Since currently /var is entirely from /dev/sda7 (my original lvm
    partition) should I use the optional parameter to lvextend to
    force the new space for /var to come from there as well?
        lv extend --size +10G /dev/sda7

thanks in advance
allan


==================== from Alan McKinnon ==============================

Let's look first at the layers of stuff involved:


   files & directories

   file system

   logical volume (LV)

   volume group (VG)

   physical volume (PV)  

   physical partition    (i.e. /dev/sda1 etc)

   physical disk         (i.e. something Seagate etc made)

OK, there's a lot of stuff there. When you made the LV, you worked from
the bottom up

Nothing in that list can be bigger than the thing below it.