From a few notes here and there, I've been under the impression that multiple snapshots of a single LV are possible. The problem is that whenever I try to take more than two, everything falls apart.
I'm running Debian unstable, kernel 2.4.20, with the following packages: kernel-patch-device-mapper 1.00.03-1 libdevmapper1.0 1.00.03-1 lvm2 2.00.06-1 lvm-common 1.5.9.3
I've also applied the linux-2.4.20-VFS-lock.patch from the device-mapper 1.00.05 tarball at sistina.
The kernel compiles fine and dm-mod loads. I've run devmap_mknod.sh from the tarball as well, and I can create PVs, VGs and LVs. I can make file- systems on them which survive reboots, and everything looks fine.
I have a shell script which creates a snapshot named for the current time: === #!/bin/bash WHEN=`date "+%Y%m%d%H%M%S"` lvcreate -L 4M -s -n $WHEN /dev/vg0/lv0 mkdir /test/snap/$WHEN mount /dev/vg0/$WHEN /test/snap/$WHEN ===
So, here's an example session which demonstrates my problem. Everything looks fine until the third snapshot, which gives an I/O error when I try to mount it, and also appears to trash the first snapshot - "ls -la" doesn't even list "." or ".."!
test:~# pvcreate /dev/hdb Physical volume "/dev/hdb" successfully created
test:~# vgcreate -s 256k vg0 /dev/hdb Volume group "vg0" successfully created
test:~# lvcreate -L 512m -n lv0 vg0 Logical volume "lv0" created
test:~# mke2fs /dev/vg0/lv0 [SNIPPED - Believe me, it worked fine]
test:~# mount /dev/vg0/lv0 /test/fs
test:~# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/hda2 841340 742420 56184 93% / /dev/mapper/vg0-lv0 507748 13 481521 1% /test/fs
test:~# ./snap Logical volume "20030910123716" created
test:~# cp -R * /test/fs/
test:~# sync
test:~# ./snap Logical volume "20030910123756" created
test:~# rm -rf /test/fs/src/
test:~# ./snap Logical volume "20030910123812" created /dev/vg0/20030910123812: Input/output error mount: you must specify the filesystem type
test:~# ls -la /test/snap/20030910123716/ total 0
test:~# ls -la /test/snap/20030910123756/ total 22 drwxr-xr-x 4 root root 1024 Sep 10 12:37 . drwxr-xr-x 5 root root 4096 Sep 10 12:38 .. drwx------ 2 root root 12288 Sep 10 12:37 lost+found -rwxr-xr-x 1 root root 62 Sep 10 12:37 makelv0 -rwxr-xr-x 1 root root 41 Sep 10 12:37 makelv0~ -rwxr-xr-x 1 root root 166 Sep 10 12:37 snap -rwxr-xr-x 1 root root 151 Sep 10 12:37 snap~ drwxr-xr-x 5 root root 1024 Sep 10 12:37 src
test:~# ls -la /test/snap/20030910123812/ total 8 drwxr-xr-x 2 root root 4096 Sep 10 12:38 . drwxr-xr-x 5 root root 4096 Sep 10 12:38 ..
Thanks, glen.
-- | Nine megs for the secretaries fair, | One disk to rule them all, | | Seven megs for the hackers scarce, | One disk to bind them, | | Five megs for the grads in smoky lairs, | One disk to hold the files | | Three megs for system source; | And in the darkness grind 'em. | ----------------------------------------------------------------------------- | Glen Harris | glen@gbrmpa.gov.au | 07 47500893 | http://www.gbrmpa.gov.au | -----------------------------------------------------------------------------
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