[PS] C:\Windows\system32>$dbs = Get-MailboxDatabase
[PS] C:\Windows\system32>$dbs | foreach{Get-MailboxStatistics -Database $_.Name | where {$_.Displayname -like "*test*"} | select Identity, Displayname, TotalItemSize, Database, Disconnect*}


Identity         : d7e6d88b-a905-4a6a-bf7d-270b64e734f3
DisplayName      : Test User01
TotalItemSize    : 4.795 GB (5,148,164,291 bytes)
Database         : DB14
DisconnectDate   :
DisconnectReason :

Identity         : c0265cf0-8935-419a-921c-107095aa908b
DisplayName      : Test User02
TotalItemSize    : 4.04 GB (4,337,656,320 bytes)
Database         : DB15
DisconnectDate   :
DisconnectReason :

Identity         : 9fdeb360-933f-4c5c-be2a-4f20141df548
DisplayName      : Test User03
TotalItemSize    : 4.713 GB (5,060,934,314 bytes)
Database         : DB15
DisconnectDate   :
DisconnectReason :

Identity         : 277b608e-69e3-49c7-9be8-2e0123cdddb7
DisplayName      : Test User04
TotalItemSize    : 10.9 GB (11,700,122,189 bytes)
Database         : DB16
DisconnectDate   :
DisconnectReason :