prepISO + ntfs external drive + ps2 isos

https://youtu.be/iSt6VpxE2c8?is=e6OV_nJROrKq2pdh

on cfw recently and used this method for psx, ps2, and ps3 games.

Question: with the ps2 games copying from external drive to internal, am i ok to then delete them from my external hard drive? ... or the ps2 iso still needs to be on the external drive?