Logical Volume Manager frequently asked questions:                   05/26/1998
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Q1: i can't create my volume group "mygroup"

A1: you can't create a volume group with the same name as an existing one.
    You can't create more than 8 volume groups at this point in time.
    You are only able to use inititalized physical volumes (see pvcreate(8)).


Q2: i can't create a physical volume with pvcreate(8)

A2: maybe pvcreate(8) complains that the physical volume has already
    been initialized. So... think about "pvcreate -f[f] ...".
    But DON'T DO THAT, if the physical volume belongs to another volume group!


Q3: i'm not able to extend a logical volume.

A3: your volume group is full or you've already reached the maximum
    logical volume size in that volume group. Logical volume size depends
    on the size of the physical extends, which only can be set at
    volume group creation time.
    The default physical extend size is 4MB which limits ;-) logical
    volumes to a maximum of 65524 MB (see vgcreate(8), vgdisplay(8).
    If your volume group isn't full your logical volume may have striped
    or contiguous allocation policy. Have a look at the physical volumes
    with pvdisplay(8) to figure out, if there are no free (contiguous)
    physical extends to the logical volume extension.


Q4: i can't move my logical volume(s) away from a physical volume with
    pvmove(8).

A4: look at the free space on all destination disks you want to use AND
    at the attributes of the logical volumes to be moved.
    Remember: you can't move a contiguous logical volume when there isn't 
              enough free contiguous space on any destination disk.
              In this case you can think about changing from contiguous
              allocation policy to next free and do the attribute change
              with lvchange(8).
              You can't move a striped logical volume either, if there isn't
              enough space for the complete stripe on any destination
              physical volume.
              You can't move to physical volumes which are NOT allocatable.
              Think about changing this with pvchange(8).


Q5: my striped logical volume works horrible slow...

A5: if you put it on two or more physical volumes based on partitions on
    one disk, you are not able to gain performance.
    Remember: you are allowed to use two or more partitions of one disk as
              physical volumes (this only makes sense for next free
              allocated logical volumes on those physical volumes).
              If you have attached two IDE disks to one adapter, you can't
              get parallel i/o on these two disks.


Q6: i'm not able to rename my volume group / logical volume.

A6: you have to deactivate them before you are allowed to rename them
    (see lvrename(8), vgrename(8)).


Q7: "make install" gives me a  "Fatal ERROR: invalid OS version"

A7: for LVM to be able to remap physical extends to blocks on disk(s)
    /usr/src/linux/drivers/block/ll_rw_blk.c and perhaps
    /usr/src/linux/drivers/block/ksyms.c have to be changed while
    LVM is in it's alpha phase. Have a look at the steps described
    in INSTALL.


Q8: a LVM command was just working when my system crashed...

A8: bring your system back online and look at the volume group
    backup files in /etc/lvmconf.
    There's at least one called /etc/lvmconf/VolumeGroupName
    (and perhaps another called /etc/lvmconf/VolumeGroupName.conf).
    You can use these backup files to bring the configuration
    back to the one before the crash (see vgcfgrestore(8)).
