First of all: There are no hard drives greater than 500 GB available in the moment. If you mean one of these uber-drives from LaCie, which have 2 TB in a portable case, they should work fine I guess. They work via FireWire, where there's basically no limitation in size, also, OS X/Server is a Unix based OS, which also should support drives of that size.
According to THIS ARTICLE the limitation for volume size with 10.3 server is 16 TB. I wasn't able to find any change for Tiger, but it would be that or higher. Note that that covers volume size, and not disk capacity. As a volume of that size will not be on just one disk, the disk capacity becomes irrelevant to the operating system in use (or just a function of the disk controller). As HomunQlus pointed out, drives larger than 500GB are not yet available.
maybe I should have used volume instead of capacity. anyway, I'm trying to test if Tiger would support my RAID volume which is more than 2TB. If HFS+ would support that large volume.
I know that it's not only the filesystem that could tell if a system could support more than 2TB volume, but also the hardware, basically the PROM, firmware, etc. So, does G5 support more than 2TB volume?
The maximum volume size is not a hardware-imposed limit. It is an OS-imposed limit. If you have OS X 10.3 or later, then that limit is 16TB per volume. You would have to check with whoever provides your RAID system controller to see if there is any limitation through that gear. That will need a whole bucket-full of hard drives to provide enough space for a 16TB volume.
The G5 processor can handle the needs of the drive controllers.
well what I mean is that, its because of LBA. basically the there are 512bytes in one sector. that sector has a 4bytes address. which gives you 2TB capacity. so in order that filessystems could overcome the 2TB mark, they made a 16bytes address, so filesystems access them in multiple of 512bytes, 4k, 16k..etc.
so if there is a 64bit LBA...basically it wud support your volume naturally...