Knowing free mdb space

Hello,

I have recently migrated my openldap server from hdb to mdb. In this kind of database you configure the maximal database size with maxsize option.

Although I have configure this option with 8GB, more than the double of my actual database size, I would like to know if there is any way to calculate the remaining size.

According to [1] you can get the actual size with a du. But my problem is that I'm using zfs with a compressed file system, so du reports the compressed size, not the real one.

Is there any way to get this value? Or my real maximum size is 8GB after compression?

[1] https://wiki.zimbra.com/wiki/OpenLDAP_Performance_Tuning_8.0