In dCacheSetup (in Aglt2,  it is poolSetup)you need to define:

metaDataRepositoryImport=org.dcache.pool.repository.meta.file.FileMetaDataRepository
metaDataRepository=org.dcache.pool.repository.meta.db.BerkeleyDBMetaDataRepository

Then you need to restart your pool *once*.

After that you remove the declaration of metaDataRepositoryImport from 
dCacheSetup (but leave the metaDataRepository declaration in place). You 
restart your pool again.

The first restart will be as slow as always. The second restart will be 
much faster and the pool will use less memory.

Once you have moved to the DB backend, it is important that you do not 
switch back - otherwise the pool looses all the meta data.

Be warned that the DB backend stores all data in a database - if that 
database is corrupted, the pool may need to refetch all information from 
PNFS/Chimera. It will also loose information about pins.