[linux-lvm] meaning of -L for snapshots ?

[Olivier Kaloudoff]

Hello,

 	I'm playing with lvm snapshots for the first time,
and wondering the meaning of -L when creating a snapshot. Indeed,
the following example shows a snapshot done with -L10M, on a
volume that's already 156M used for a total of 2G;


[root at shinwey root]# df /vservers/skel/ -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/nr_180/skel      2.0G  156M  1.8G   9% /vservers/skel

[root at shinwey root]# lvcreate  -L10M --snapshot --name snaptest 
/dev/nr_180/skel
lvcreate -- rounding size up to physical extent boundary
lvcreate -- WARNING: the snapshot will be automatically disabled once it 
gets full
lvcreate -- INFO: using default snapshot chunk size of 64 KB for 
"/dev/nr_180/snaptest"
lvcreate -- doing automatic backup of "nr_180"
lvcreate -- logical volume "/dev/nr_180/snaptest" successfully created

[root at shinwey root]# mount /dev/nr_180/snaptest  /mnt/snaptest/
mount: block device /dev/nr_180/snaptest is write-protected, mounting 
read-only

[root at shinwey root]# df -h /mnt/snaptest/
Filesystem            Size  Used Avail Use% Mounted on
/dev/nr_180/snaptest  2.0G  156M  1.8G   9% /mnt/snaptest



 	Who can explain the usage of -L10M for my snapshot ?


Best Regards,


Olivier Kaloudoff