Tiger & Maximum Hard Drive Size?

Internally, yes, if you have a 2002 QuickSilver or later model. All earlier models only support a maximum of 128 GBs per drive or partition (you can install larger drives, but the drive must be partitioned into volumes no larger than 128 GBs.) After 2002 this limitation was removed by having a new disk controller installed on the motherboard.

There should be no limitations using an eSATA controller. At this point in time the largest drive on the market is 1.5 TBs, although Hitachi has just announced a 2 TB drive. I don't know if it's in the distribution chain as yet.

Barring any IDE/ATA limitations and like Kappy says, SATA/eSata should not be affected...

http://support.apple.com/kb/HT2422

Eight ExoBytes. 🙂

http://eshop.macsales.com/item/ACARD/AEC6880M/
this RAID card will allow you to combine 2 500GB PATA drives (not sure if any larger PATA capacities are available) as one large volume, with faster read/write performance than a single drive. The striped RAID option joins Master and Master drives on separate cables, and Slave and Slave drives, so you could have 2 striped RAIDS, and use one to back up the other. this card will also work with OS 9 (might not matter to you)

you will also need longer cables
http://eshop.macsales.com/item/Sonnet%20Technology/TCBAGP/

For internal SATA you could put in two of these PCI cards:
http://eshop.macsales.com/item/Sonnet%20Technology/TSATA/
to support 4 internal SATA drives. I don't think any of the SATA RAID cards support OS 9, and they are a little more expensive.

Fantastic post/links/suggestion Glen, thanks! 🙂

Another external option, since you have eSATA, look at these 4-drive RAID enclosures. With RAID 5 mode enabled, you get capacity of 3 drives, and if one drive fails you can hot swap it without losing any data, even rebuilds data without the computer on. You also get a little faster performance. So you get 75% usage of the drives with data security instead of 50% usage with a traditional backup scheme or mirroring. Another option to think about.

http://eshop.macsales.com/shop/hard-drives/RAID/Desktop/

All depends on your budget and how much data storage you need...just don't forget the backup drives also.

Which eSATA card are you using? How many unused PCI slots do you still have?