Error when I compare hashes of export-diff / import-diff

Rafael Diaz Maurin <Rafael.DiazMaurin@xxxxxxxxxxxxxxx> · Tue, 11 Jun 2019 15:24:20 +0200

Hello,

I have a problem when I want to validate (using md5 hashes) rbd 
export/import diff from a rbd source-pool (the production pool) towards 
another rbd destination-pool (the backup pool).

Here is the algorythm :
1- First of all, I validate that the two hashes from lasts snapshots 
source and destination are the same :
rbd -p ${POOL-SOURCE} export ${KVM-IMAGE}@${LAST-SNAP} - | md5sum
=> 3f54626da234730eefc27ef2a3b6ca83
rbd -c ${BACKUP-CLUSTER} -p ${POOL-DESTINATION} export 
${KVM-IMAGE}@${LAST-SNAP} - | md5sum
=> 3f54626da234730eefc27ef2a3b6ca83

2- If not exists, I create an empty image in the destination pool
rbd -c ${BACKUP-CLUSTER} create ${POOL-DESTINATION}/${KVM-IMAGE} -s 1

3- I create a snapshot inside the source pool
rbd snap create ${POOL-SOURCE}/${KVM-IMAGE}@${TODAY-SNAP}

4- I export the snapshot from the source pool and I import the snapshot 
towards the destination pool (in the pipe)
rbd export-diff --from-snap ${LAST-SNAP} 
${POOL-SOURCE}/${KVM-IMAGE}@${TODAY-SNAP} - | rbd -c ${BACKUP-CLUSTER} 
import-diff - ${POOL-DESTINATION}/${KVM-IMAGE}

The problem occurs when I want to validate only the diff between the 2 
snapshots (in order to be more efficient). I note that those hashes are 
differents.

Here is how I calcultate the hashes :
Source-hash : rbd diff --from-snap ${LAST-SNAP} 
${POOL-SOURCE}/${KVM-IMAGE}@${TODAY-SNAP} --format json | md5sum | cut 
-d ' ' -f 1
=> bc56663b8ff01ec388598037a20861cf
Destination-hash : rbd -c ${BACKUP-CLUSTER} diff --from-snap 
${LAST-SNAP} ${POOL-DESTINATION}/${KVM-IMAGE}@${TODAY-SNAP} --format 
json | md5sum | cut -d ' ' -f 1
=> 3aa35362471419abe0a41f222c113096

In an other hand, if I compare the hashes of the export (between source 
and destination), they are the same :

rbd -p ${POOL-SOURCE} export ${KVM-IMAGE}@${TODAY-SNAP} - | md5sum
=> 2c4962870fdd67ca758c154760d9df83
rbd -c ${BACKUP-CLUSTER} -p ${POOL-DESTINATION} export 
${KVM-IMAGE}@${TODAY-SNAP} - | md5sum
=> 2c4962870fdd67ca758c154760d9df83

Can someone has an idea of what's happenning ?

Can someone has a way to succeed in comparing the export-diff /import-diff ?

Thank you,
Rafael

--
Rafael Diaz Maurin
DSI de l'Université de Rennes 1
Pôle Infrastructures, équipe Systèmes
02 23 23 71 57

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