Snapvault lag question

[IlyaPykhov]

Dear members,

Could you please help me with one questions, we had the lag of 54 days for one snapvault relation due to slow network speed, after changing the line to faster one, the snapvault was restarted and transfer was successfully done. So, the question is, what data was transferred between primary and secondary (the size was quite big)? Was it all data for those missed 54 days?

Thanks in advance.

[robinpeter]

while you transfer 1st time.. the volume will be replicated to your secondary volume.

after the base line.. snapvaule will be transferring the delta between last transfer (that's the concept)

and its calculated using snapshots.

again.. depends on your ontap version.. there are more changes.

If you are using clustered ontap, delta is calculated in block level..

which mean.. if you have a 10GB file and one block of that file is changed.. only those changed block will be transferred to secondary.

in 7-Mode, delta calculated in file level, so it will transfer the entire 10G file (just because one block on that file is changed)

hope that help.

robin.

[IlyaPykhov]

Hi Robin,

Thanks for information. We are using Data Ontap 8.2.4P5 7-Mode, here is the situation which I need to understand:

1. SV lag is 1 month
2. Last successful SV transfer was done, e.g. on 01/03/2017 
3. SV was resumed, e.g. on 01/04/2017

Will it copy all chaged files from the source by comparing the last successful SV copy (01/03/2017) on the destination with file system state on 01/04/2017? So, all the changed files in the period of 1 month are going to be copied to destination, am I correct here?

Thanks in advance.

[robinpeter · Accepted solution]

If the configurations are correct.. Yes, it will.. 

You can use "snap delta" command on your secondary to see how much data in transfer.

even though it dont give much clarity.. you can use that number.. and compare against the delta in primary system.

each time.. snapvault create a snapshot in pimrary and compare it it against the previous snapshot it created for last transfer.

thats how its claculate the delta. In primary volume you will be able to see those snapshots, using snapshot status command

by the end of a successful transfer snpvault delete the old snapshot from primary and rename the new snapshot and keep it.(which was created starting of this transfer)

so it can be used to calculate the delta for next transfer.

hope that answer your question.