Sql-server – SQL Server data drive (.mdf files) running out of space

Space is available inside the database because data has been moved around. Perhaps you have very high levels of page splits, or have recently deleted a large portion of data that had previously caused the data file to grow.

SQL Server does not shrink database files automatically when you've freed up space within them, because the logical assumption is that if you've used that space once, you'll use it again. Autogrow can be an expensive event and unnecessary if you've only freed up space temporarily (what were you able to do with all that free space in the meantime?). For the same reasons, you shouldn't try to temporarily reclaim space, either. Just let SQL Server use the 18 GB of available space as you add more data. If you think you will need more than 18 GB of additional space going forward (in which case, you will need to add file(s) on other disks, or move to a bigger disk).

sp_spaceused (and in turn the UI dialog you're looking at) may return more space than is possible because of synchronization issues in the metadata about your tables/indexes/files. In order to make sure it reflects accurate space, run this:

DBCC UPDATEUSAGE(0);

I have also seen scenarios where rebuilding indexes was required in order to rectify the counts/space, but I haven't seen that specific case since SQL Server 2000.

(I suspect this isn't a simple case where your database already spans multiple disks, or you surely would have mentioned that in the question.)

That all said, the fact that when you shrink the data file expands almost immediately leads me to believe that you are actually using the space, but must also be performing big deletes or updates that are freeing it up (which is when you see 18 GB free). Unfortunately it's impossible for us to see exactly why the data file is expanding and then clearing itself out - perhaps you have transactions where you are truncating / re-populating large tables, performing massive archive operations, etc.

If you've dropped all the tables, you could just drop the database and re-create it. It will be created with the default sizes and growth rates as defined by the model database. These may not be ideal (I don't find the defaults particularly useful in most scenarios), but you can change them.

Unless you have a lot of things set up on this database (like Service Broker, a ton of users, etc.), I think that is less cumbersome than getting into the habit of growing/shrinking growing/shrinking growing/shrinking. You should put the database on a drive that has enough space to accommodate the data you're going to generate, without having to shrink all the time. Shrinking and growing are both expensive events, especially on slow I/O.

Also, to prevent the log from growing to 9 GB (that seems pretty ridiculous for the data you describe), you should either be full recovery and you need to perform more frequent backups and log backups, or you should switch to simple recovery. More details here - it's long but please read it all.