Logical Volume Manager frequently asked questions:                   06/28/1998
--------------------------------------------------

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!
    Remember to set the partition system id to 0xfe with fdisk(8) before
    trying pvcreate(8) on it.


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 256 GigaByte (see vgcreate(8), vgdisplay(8)).
    If your volume group isn't full or you didn't reach the current
    logical volume size limit, your logical volume may have striped
    or contiguous allocation policy. Have a look at the physical volumes
    with vgdisplay or pvdisplay(8) to figure out, if there are not enough
    free (contiguous) physical extends.


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
    (or which are implicit used) 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)).


Q9: why are my logical volumes limited to 256 GB in size

A9: this is NO absolute limit but it depends on the physical extend size you
    configured at volume group creation time.
    Please use option -s of the vgcreate command to give a larger physical
    extend size. For example with a physical extend size of 524288 KB (512 MB)
    you are able to map a logical volume of 32 TeraByte.


Q10: i can't split my volume group my_vg

A10: the physical volumes you want to split of into another volume group
     may NOT have logical extends of logical volumes staying in the original
     vloume group you started with. Please use pvmove to achieve this.


Q11: i can't merge my two volume groups my_vg1 and my_vg2

A11: a merged volume group can't go beyond the physical or logical volume
     limits of the destination volume group. This means for egg. that you
     can't merge my_vg1 with 20 logical volumes and my_vg2 with 30 logical
     volumes getting my_vg1, if my_vg1 has a 31 logical volume limit.
     You are only able to merge (up to now) volume groups with equal
     physical extend sizes.

