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

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On 6/11/19 3:24 PM, Rafael Diaz Maurin wrote:
> 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}

Here, you are wrong
If have to export-diff (without --from-snap) to do the "first" export
What you are doing is rebasing the image, on the backup cluster, based
on crap (the dummy snapshot you created on step 3)

So:
1) Create a snapshot of source image
2) Create a dest image if not exists
3) If dest was created, export the source snapshot and import it:
  rbd export-diff <image> --snap <snap> | rbd import-diff - <dest-image>
3b) If dest was not created (you then have a shared snapshot between the
source and the dest), export-diff using from-snap:
   rbd export-diff --from-snap <snap1> <image> --snap <snap2> | rbd
import-diff - <dest-image>

You can checkout Backurne's code, that does what you want:
https://github.com/JackSlateur/backurne/blob/master/ceph.py#L173

Best regards,

> 
> 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
> 
> 
> _______________________________________________
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> ceph-users@xxxxxxxxxxxxxx
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> 
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