We have NAS server FS8600 and used space on 4 vols are less than 20TB.
But in SC8000 array, NAS vols show about 35TB. Dell techs say this is because of white space on array, space needs to be reclaimed through SCSI Unmap on NAS server. So I turned it on and it's been 6 days after that and I expired last 5 day worth snapshots because they grow dramatically filling up vols in array. snapshots in NAS side hasn't changed. However, the discrepancy between SC8000 and FS8600 is still large.
SAN:
SC8000
NAS Volumes: Vol 1,2,3,4
Configured Space: 60TB handed off to NAS
Active Space: 36TB
Snapshots: 2TB (Reduced from 5.5TB last night by manually forcing to expire)
Raid Overhead: 10TB
NAS
FS8600 FluidFS 5.0
NAS Pool: 60TB
Configured: 40TB
Used Space: 18TB
Snapshots: 250GB