[linux-lvm] snapshot problem when memory size is over 4GB

Chung Hsien Hu mozo at coventive.com
Thu Mar 3 09:50:51 UTC 2005

I got a server with Tyan5350 mainboard and 8GB ECC RAM. And
it seem that snapshot didn't work in either LVM1 or LVM2 when
the memory over 4GB is plugged. We have HIGHMEM64G=y kernel
option been set. Everything is ok when the comination is
"snapshot + 4GB RAM" or "no snapshot + 8GB RAM"...
Any clues?
PS: Hope you could understand my question, english is not my
mother language. :(

1. in linux-2.4.27 + LVM-1.0.8, it failed to activate the VG with
any existed snapshot volume.
bash-2.03# vgchange -ay
vgchange -- ERROR "Bad address" activating volume group "storage"

2. And again, in linux-2.4.27 + LVM-1.0.8, it failed to create snapshot
bash-2.03# lvcreate -A n -s  -n test_snap -l 16 /dev/storage/test
lvcreate -- WARNING: the snapshot will be automatically disabled once it 
gets full
lvcreate -- INFO: using default snapshot chunk size of 64 KB for 
lvcreate -- ERROR "Cannot allocate memory" creating VGDA for 
"/dev/storage/test_snap" in kernel

3. Then I turn to test linux-2.6.10 + LVM2. This time I can create a 
snapshot and it work well until
I reboot the system. The system will crash when I try to make a tarfile 
over the original volume.

bash-2.03# lvm version
  LVM version:     2.00.31 (2004-12-12)
  Library version: 1.00.19-ioctl (2004-07-03)
  Driver version:  4.3.0
bash-2.03# lvm lvscan
  ACTIVE   Original '/dev/storage/test' [1.95 GB] inherit
  ACTIVE            '/dev/storage/xfs' [1.95 GB] inherit
  ACTIVE   Snapshot '/dev/storage/test_snap' [500.00 MB] inherit
  ACTIVE            '/dev/storage/sysvolume' [2.44 GB] inherit
bash-2.03# tar cvf /mnt/xfs/test.tar /mnt/test
a /mnt/test/ directory
a /mnt/test/ACARD101RC3.iso 67534848 bytes, 131904 tape blocks
===>SYSTEM CRASHED!!......
system halt and the last line of messages on screen is:
<0>Kernel panic - not syncing: Fatal execption in interrupt

It's interesting to mention that the snapshot work well before reboot. Seem
it is kind of problem relate to VFS cache, snapshot and HIGHMEM support?

Mozo Hu. mozo at coventive
R&D Assistant Manager, Coventive Advance Technologies

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