BIG.DAT

From Redump Wiki

PlayStation "DRM" by Datel, assumedly used to defeat PS2 disc authentication checks.

Has intentional errors present near the start of the disc, similar to safedisc.

Should be handled by redumper.

If a datel PS2 disc has errors but big.dat is not identified, mainly on later Japanese action replay max discs, it may be another scheme of big.dat.