Moving MyISAM database from mysql 5.0 to 5.1

[友和 大村]

Hello,

I have two x86/x86_64 servers running RHEL5.3(32bit) and RHEL6.3(64bit).
As the server for RHEL5 become old, I need to migrate my
MyISAM database to RHEL6. Would there be issues copying the whole
/var/lib/mysql directory to RHEL6 and execute mysql_update ?

I can't use mysqldump because the database is about 5TB in total.
I'm pretty sure it's going to take days to backup and restore.

I've been reading many documents on the MySQL website, but all doesn't seem to give me the precise answer.

The MySQL I'm using is the following.

mysql-server-5.0.45-7.el5
mysql-server-5.1.61-4.el6.x86_64

Please advise,
Thanks.