SnapShot size same Data size

[MAGIC_PIG]

We are use NetApp 2750 Ontap 9.7p7 . Volume is use for CIFS.  Volume size is 800GB. Data only use 410GB  But we have problem one of snapshot is use 401.41GB. Can any one tell me how to find out root cause. Now I need expand volume to 1TB.  We are worry snapshot again will mark volume no space. 

[paul_stejskal]

https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/What_can_impact_snapshot_size_and_cause_snapshot_spill

https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/Snapshots%3A_including_SnapShot_Issues_and_Solutions

See if that helps. Basically you'll have to investigate the file system for changes. If it is a NAS volume this may be harder unless you have FPolicy or Auditing enabled. For a SAN volume you'll have to check from the SAN client. Since it's a SnapMirror it is unclear if this is a source or destination volume so you may have to check the source for any changes if this is the destination.