You are limited to the auto-generated backup filename when doing Fast Compression.
We have logged an enhancement request LS-1002: "ability to name fast compression backups. Ability to use any naming format or LiteSpeed variable."
The 'Backup Name' field of the 'Select Backup Type' UI screen--that field is not what it appears to be. That UI screen says "optional property that describe the backup...is an internal property of the backup, it is not used to create the actual file name on disk."
It could seem like a UI defect that the field is even enabled for Fast Compression backups (since the field doesn't do anything, why even have it). Its actually not a defect because whatever you put in that field doesn't actually impact what you probably think it does.
The UI screen on which you actually set the name format is 'Backup Destination' in the "Backup file name format field". That UI screen is available only if earlier in the Wizard, you had chosen "Full" backup type. That UI screen is not present for "Fast Compression" backup type.
(T-log screen, even with Fast Compression mode chosen, lets you use LiteSpeed variables in a T-log backup name)
