Q:

How to convert a reiserfs partition to ext3?

Is there a tool to convert a reiserfs partition to ext3?

A:

Since it's recommended anyway to have backups before filesystem conversions, you'd better copy everything (do not forget file permissions) somewhere, create an ext3 filesystem on that partition, then copy everything back.

A:

Converting between filesystems is generally not possible. If you have space constraints your best bet is to

either get an external storage to migrate
use squashfs if you have just enough storage for a compressed image available

