cksums don't match directly following lvm snapshot

Defested · 06-16-2015, 04:29 PM

I am attempting to create a lvm snapshot of a filesystem The commands to do so are

Code:

umount /epoch/dr/db
lvremove /dev/MVM/lvdr -f
lvcreate --size 3G --snapshot --name lvdr /dev/mapper/MVM-lvprddb
mount -onouuid /dev/mapper/MVM-lvdr /epoch/dr/db

however, directly after making the snapshot volume, the checksums of some of the files don't match. Here is the output

Code:

[root@mvm /]# umount /epoch/dr/db
[root@mvm /]# lvremove /dev/MVM/lvdr -f
  Logical volume "lvdr" successfully removed
[root@mvm /]# lvcreate --size 3G --snapshot --name lvdr /dev/mapper/MVM-lvprddb
  Logical volume "lvdr" created.
[root@mvm /]# mount -onouuid /dev/mapper/MVM-lvdr /epoch/dr/db
[root@mvm /]# cksum /epoch/dr/db/app/APP.DAT
2877706219 19451084800 /epoch/dr/db/app/APP.DAT
[root@mvm epic]# cksum /epoch/prd/db/app/APP.DAT
2819183329 19451084800 /epoch/prd/db/app/APP.DAT
[root@mvm /]# lsof /epoch/dr/db/app/APP.DAT
[root@mvm /]# lsof /epoch/prd/db/app/APP.DAT
[root@mvm /]#

per the above lsof command, there are no processes that would be editing these files...

This is on a CentOS7 box.

Any ideas?

JeremyBoden · 06-17-2015, 06:22 PM

Note that your byte counts are unchanged in your cksum's...

Defested · 06-24-2015, 02:43 PM

Quote:

Originally Posted by JeremyBoden

Note that your byte counts are unchanged in your cksum's...

Yes, that is true, but the MD5sums are different which is the horrifying part.

JeremyBoden · 06-24-2015, 05:38 PM

What is the effect of the nouuid option?
Does this mean you are reading the snapshot or the un-snapshotted file?

Defested · 07-20-2015, 03:40 PM

Quote:

Originally Posted by JeremyBoden

What is the effect of the nouuid option?
Does this mean you are reading the snapshot or the un-snapshotted file?

With LVM snapshots, the snapshot volumes do not have a separate UUID from the source volumes. mount complains that the snapshot volume's UUID is already in use, this bypasses that check.