[CentOS] strange partitioning problem

Hello listmates,

Here's I am, trying to install Centos 6.2 64-bit on a server with 24 TB of
disk RAIDed as RAID 6. So I get this 18 TB disk (the RAID is recognized as
one disk) where I am trying to put my OS. And I can create a couple of
partitions - let us say I defiine a 150 GB swap, a 150 GB "/", a 100 GB
"/var". So far so good. Then I try to define the next one, say, a 100 GB
"/tmp" and get a message stating there is not enough disk space whereas I
still have over 18 TB free and the installation interface reflects that
accurately!

I am at a loss. Is that something related to the sheer size of the disk?
Why would this happen - especially at so basic a stage of the process?

At any rate, any help or advice would be greatly appreciated.

Regards,

Boris.