[linux-lvm] LVM snap size weirdness...

[Barry, Christopher]

All,
	See output of lvdisplay below...

lvm> lvdisplay
  --- Logical volume ---
  LV Name                /dev/vg0/data
  VG Name                vg0
  LV UUID                fox8qK-dePL-xTi1-zfBO-xQzu-R5Ls-yZ5bgQ
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                200.00 GB
  Current LE             51200
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:0

  --- Logical volume ---
  LV Name                /dev/vg0/home
  VG Name                vg0
  LV UUID                C748g0-PYnB-zdtB-p1Eh-kYIU-1zXN-n1yKsb
  LV Write Access        read/write
  LV snapshot status     source of
                         /dev/vg0/homeSnap [active]
  LV Status              available
  # open                 1
  LV Size                200.00 GB
  Current LE             51200
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:1

  --- Logical volume ---
  LV Name                /dev/vg0/installs
  VG Name                vg0
  LV UUID                yKoPPg-BM0J-245e-BgCZ-kj3m-DVSo-5edFbH
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                200.00 GB
  Current LE             51200
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:2

  --- Logical volume ---
  LV Name                /dev/vg0/vortex
  VG Name                vg0
  LV UUID                slyYlF-tU41-rLmt-y7eC-GU41-iWD3-bsnFil
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                800.00 GB
  Current LE             204800
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:3

  --- Logical volume ---
  LV Name                /dev/vg0/homeSnap
  VG Name                vg0
  LV UUID                1eaqQh-DtCf-1FD7-iUwx-UHzR-aH0G-4X2BQv
  LV Write Access        read only
  LV snapshot status     active destination for /dev/vg0/home
  LV Status              available
  # open                 1
  LV Size                200.00 GB
  Current LE             51200
  Segments               1
  Snapshot chunk size    8.00 KB
  Allocated to snapshot  0.00%
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:10

lvm>


After creating the snapshot vg0/homeSnap, mounting it, and viewing it, everything looked fine. But a df (below) shows something is amiss. Look at the size on the homeSnap vs the size of the DATA lv. For some reason they are identical, yet the snap contains the data from the HOME lv.


debian:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/hda2             942M  688M  207M  77% /
/dev/hda1              46M  4.6M   39M  11% /boot
/dev/hda5             9.2G  875M  7.9G  10% /usr
/dev/hda6             1.9G  155M  1.6G   9% /var
/dev/hda7             5.4G   33M  5.1G   1% /sys_data
/dev/vg0/data         200G   32G  169G  16% /mnt/lvm/data
/dev/vg0/home         200G  102G   99G  51% /mnt/lvm/home
/dev/vg0/installs     200G  5.9G  195G   3% /mnt/lvm/installs
/dev/vg0/vortex       800G  3.2M  800G   1% /mnt/lvm/vortex
/dev/vg0/homeSnap     200G   32G  169G  16% /mnt/lvm/home-snap


I have dumped an ls of both the snap lv and the home lv and diffed them - no differences.
Why/how can df be confused?




Thanks for your help,
Christopher