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[linux-lvm] Single snapshots do weird things?



Since my last message to the list, when I found I was using an old
version of the driver(4.0.2), I've done a completly new install
of the kernel.org 2.4.21 sources, and the device-mapper.1.00.05 and
LVM2.2.00.06 tarballs. This is still on Debian unstable, but no
Debian lvm packages or kernel patches are installed this time.

I've patched the kernel with the device-mapper and VFS patch,
compiled and installed both tarballs, and can insmod the dm-mod
with no errors.

Now, when I copy 2Mb onto the filesystem and create an 8Mb snapshot,
it's immediately flagged INACTIVE, "Allocated to snapshot" is 100%
and is not mountable.

I'm using a 256k PE size and a 512Mb LV on a 10Gb disk.

Here's the sequence of commands, with output omitted where the command
works normally.

lvm:~# pvcreate /dev/hdb
lvm:~# vgcreate -s 256k vg0 /dev/hdb
lvm:~# vgdisplay vg0
  --- Volume group ---
  VG Name               vg0
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                256
  Cur LV                0
  Open LV               0
  Max PV                256
  Cur PV                1
  Act PV                1
  VG Size               9.54 GB
  PE Size               256.00 KB
  Total PE              39092
  Alloc PE / Size       0 / 0
  Free  PE / Size       39092 / 9.54 GB
  VG UUID               w7c4AZ-nmm5-BI4q-#OAm-yvSc-E0eh-#dRhSk

lvm:~# lvcreate -L 512m -n lv0 vg0
lvm:~# lvdisplay /dev/vg0/lv0
  --- Logical volume ---
  LV Name                /dev/vg0/lv0
  VG Name                vg0
  LV UUID                fAfvNg-fBhr-DCWS-Gwm6-RWfX-hHpz-EPi7zn
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                512.00 MB
  Current LE             2048
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:0

lvm:~# mke2fs /dev/vg0/lv0
lvm:~# mount /dev/vg0/lv0 fs
lvm:~# df -k fs
/dev/vg0/lv0            507748        13    481521   1% /root/fs
lvm:~# cp -R /usr/src/device-mapper.1.00.05* fs
lvm:~# sync
lvm:~# df -k fs
/dev/vg0/lv0            507748      2028    479506   1% /root/fs
lvm:~# lvcreate -s -L 8m -p r -n snap0 -d -v /dev/vg0/lv0
    Setting chunksize to 16 sectors.
    Finding volume group "vg0"
    Creating logical volume snap0
    Archiving volume group "vg0" metadata.
    Creating volume group backup "/etc/lvm/backup/vg0"
    Found volume group "vg0"
    Loading vg0-snap0
    Found volume group "vg0"
    Zeroing start of logical volume "snap0"
    Found volume group "vg0"
    Removing vg0-snap0
    Found volume group "vg0"
    Found volume group "vg0"
    Found volume group "vg0"
    Loading vg0-lv0-real
    Loading vg0-snap0-cow
    Loading vg0-snap0
    Loading vg0-lv0
    Creating volume group backup "/etc/lvm/backup/vg0"
  Logical volume "snap0" created
lvm:~# lvdisplay /dev/vg0/snap0
  --- Logical volume ---
  LV Name                /dev/vg0/snap0
  VG Name                vg0
  LV UUID                WL5TXy-gE0H-jQu!-BJod-XPmk-WnFL-VVgLus
  LV Write Access        read only
  LV snapshot status     INACTIVE destination for /dev/vg0/lv0
  LV Status              available
  # open                 0
  LV Size                512.00 MB
  Current LE             2048
  Segments               1
  Snapshot chunk size    8.00 KB
  Allocated to snapshot  100.00%
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:4

lvm:~# mount -t ext2 /dev/vg0/snap0 snap/
mount: block device /dev/vg0/snap0 is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/vg0/snap0,
       or too many mounted file systems

My syslog now shows

device-mapper: 4.0.4-ioctl (2003-08-30) initialised: dm uk sistina com
device-mapper: snapshot is marked invalid
EXT2-fs: unable to read superblock

Here's some version numbers:

lvm:~# lvm version
  LVM version:     2.00.06 (2003-08-20)
  Library version: 1.00.05-ioctl-cvs (2003-09-01)
  Driver version:  4.0.4

lvm:~# uname -a
Linux lvm 2.4.21-dm #1 Fri Sep 12 12:52:48 EST 2003 i686 GNU/Linux

lvm:~# gcc -v
Reading specs from /usr/lib/gcc-lib/i386-linux/2.95.4/specs
gcc version 2.95.4 20011002 (Debian prerelease)

lvm:/usr/src# lsmod
Module                  Size  Used by    Not tainted
dm-mod                 40364   7
3c59x                  25096   1
af_packet              11976   1
rtc                     6236   0  (autoclean)
unix                   14020   4  (autoclean)

Thanks, glen.




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