This may help you

( little bit from http://www.ibphoenix.com/ibp_db_corr.html )

The InterBase Server has two write modes (forced writes), synchronous and
asynchronous. Pre InterBase V6.0 the default write mode was synchronous:

gfix -write sync database.gdb
Post InterBase V6.0 the write mode is asynchronous:

gfix -write async database.gdb
Synchronous writes are known as "careful writes", in that the InterBase
engine will flush modified pages to disk on a transaction commit, and will
write the pages back to the database in the correct order (as far as the
database server is concerned) and so minimise any possible data loss.
Careful write is present in all cases, though without forced write, it's
careful only up to the Operating System file cache. Forced write has no
effect on Windows 3.1, Windows 95 and Windows 98. On Unix and NT, it causes
the operating system to bypass its file cache and send the page directly to
disk.

Artur