No, the white space in the first database is not moved to the new database when you do mailbox moves. The new database will be the size of just the mailboxes moved initially, so it should be smaller then the source database.
Exchange database white space
fsdg
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Hello,
my Exchange 2016 database have 50 GB of white space.
If I create new database on second disc and move mailboxes to new disc
does this new disc have 50 GB free space or more than 50Gb?
https://www.alitajran.com/get-mailbox-database-size-and-white-space/
Is white space only thing that counts during offline database defragmentation(or mailbox move)?