Why drop a index takes so long to do?

[Haitao Jiang]

Hi,

I have a 3GB index which includes a fulltext index on 2 columns. I
wanted to drop this fulltext index from the table, but it took
forever. Why it is so slow? Is it because MySQL basically go through
the index file (there is only one) and re-write it to another file and
then copy it back?

Any other fast way to drop a index like this?

Thanks

Haitao