Netapp snapshot

Keep in mind that the snapshot holds the blocks from a point in time.  If you delete data from the existing LUN these blocks will be held by the snapshot so that you can restore the snapshot to the state where it was when it was taken.

On a Netapp snapshot it's not the data that's added that makes the snapshot grow, it's the data that's deleted.  Also keep in mind that because the Netapp is a filer you have be careful when using LUNs.  If LUNs are thin provisioned you may have white space on them that will need to be cleared out by using snapdrive by using space reclaim feature

https://library.netapp.com/ecmdocs/ECMP1189419/html/GUID-721BA2A1-042E-49A4-85A5-DA734B3D1FE3.html

Will the old snapshot grow if we delete any data on the LUN?

It shouldn't grow but the usage may not shrink.  You may need to reclaim the space before you recognize any space savings on a thin provisioned LUN

I can see that old snapshot size is growing.

If you delete a snapshot that has blocks in a snapshot that took place before or after the other snapshot will grow because it needs these blocks to preserver the point in time it was taken.  Depending on how old the snapshots are this may include a good chunk of data that was deleted since then

Thank you for your reply. If I understood correctly the last snapshot will grow if there is any actives on the lun such as moving the mailboxes out if it is exchange lun?

that's correct.  If you move a mailbox from an Exchange LUN but the snapshot is holding the blocks since it was taken prior to the move, it will increase the size of the snapshot until the snapshot is cycled out.

I moved 1TB data (few mailboxes) out of that LUN and noticed that is less than 3GB. Only in increase about 1.56GB. The backup took snapshot again last night and it size in KBs.
Does this means that previous snapshot's  locks does not aware of the white space and still thinks that  there is data ? or the snapshot will increase by size when the netapp scrub runs at Sunday night?