Trying to repost own question and own answer via newsgroup interface.

> Hi, group. I use FirebirdCS 9-04p1 on Linux. My database size comes

> near 2Gb. Does anyone tried somewhat like

Alter Database Add File 'filename'
Starting at Page 250000 length 250000

>(It is 233834 pages now, page size 8192). Is it safe or I must do
> backup/restore?

If anyone more interested: just tested it, all works fine.