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Old 06-16-2015, 04:29 PM   #1
Defested
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Unhappy cksums don't match directly following lvm snapshot


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?
 
Old 06-17-2015, 06:22 PM   #2
JeremyBoden
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Note that your byte counts are unchanged in your cksum's...
 
Old 06-24-2015, 02:43 PM   #3
Defested
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Quote:
Originally Posted by JeremyBoden View Post
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.
 
Old 06-24-2015, 05:38 PM   #4
JeremyBoden
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What is the effect of the nouuid option?
Does this mean you are reading the snapshot or the un-snapshotted file?
 
Old 07-20-2015, 03:40 PM   #5
Defested
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Quote:
Originally Posted by JeremyBoden View Post
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.
 
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