This is rather an OS or disk related problem, but very unlikely caused by MaxDB.
When a Data Volume is added, MaxDB creates a file, writes some metadata into that Volume and fills the rest with hex(00) to ensure that the complete file can be written to.
If formatting is slow, then you need to check your IO system. More than an hour for just 20 GB is definitely too long and should be investigated.
If adding a a Volume aborts, then have a look into the MaxDB KnlMsg log file. There should be a MaxDB error code plus an OS error code if formatting stopped due to an OS error.
This is not related to your current problem, but please consider patching your MaxDB version 7.7.04.28 to the latest 7.7.07.xx release.
Thorsten