Replication

[idok]

Hello,
I have two storages , version FreeBSD 8.2-RELEASE-p6, I configured the same volume in the same storages - 21.4TB
I configured snapshot and replication - it's working.
freenas1 - Primary , freenas2 - Secondary .

The size (1K-Blocks) of the volume is diffrent between the storages :

freenas1
Filesystem 1K-blocks Used Avail Capacity Mounted on
FreeNAS1-local 22986515812 1863935410 21122580401 8% /mnt/FreeNAS1-l

freenas2
Filesystem 1K-blocks Used Avail Capacity Mounted on
FreeNAS2-remote 21128587319 1868909679 19259677640 9% /mnt/FreeNAS2-r

another question , why the total size of the volume is changing after replication ? the total size shouldn't be Permanent ?

Thanks
Ido

 

[peterh]

If files is added to freenas1 after the start of replication it won't be transferred ( the replication
is of a snapshot !)
You also seem to have less capacity in freenas2 by some reason.

 

[FireBIade]

The free space changing is to do with the snapshot system.

Imagine you copy some files onto your storage, the free space drops by how much space those files take and the total space remains unchanged

Then a snapshot is created so the blocks that the files take up are locked into that snapshot, again the total space remains unchanged.

Then the files are deleted but actually the data for those files still exists on the system in those locked blocks. This is the point where your total space is reduced by the size of the blocks in the snapshot.

It's only when that snapshot is deleted that the space comes back to the pool.

 

[idok]

freenas replication

hi,
thank you very much for your help.
please see the attachment file ... i still cannot understand why the total size of the volumes are differences.

 

[FireBIade]

Ok this is how I understand it

Before snapshot - Users are placing files 1,2 & 3 on the storage device through a CIFS layer onto the block storage pool underneath. Users are only aware of the CIFS layer etc.

After snapshot - The snapshot causes the blocks to become reserved because they exist in the snapshot and if we need to use the snapshot to recover the data must still exist.

After snapshot data changed - Users delete files 1 & 2 but in fact because those files still exist in a snapshot the blocks do not get released back to the pool but stay reserved. This is where your total drive space will come down, because of the reserved blocks and your snapshot size increases.

Snapshot deleted - Only when the snapshot is deleted do the blocks get returned to the storage pool and your drive space comes back again.

 

[idok]

hi,
thank you very much.
I found the problem, there was a stuck snapshot on the remote server (freenas2).
i followed the information from the url
http://serverfault.com/questions/66414/cannot-destroy-zfs-snapshot-dataset-already-exists
and now the freespace on the remote server "came back" :)
thanks again

 

[FireBIade]

Hey no probs, glad you got it sorted.