Jaz drives are SCSI devices and are available as an external drive with a 50-pin SCSI-2 self-terminating interface or an internal 3-1/2 format drive with a 50-pin header interface.
Both the internal and external devices are available in either 1 or 2 Gigabyte capacity, so there are four different Jaz drives available.
Jaz disks are a cartridge-style removable media containing a stack of three 3.5" platters. From here out, I'll be using the terms "cartridge" and "disk" interchangeably to mean the Jaz media.
The 1Gb and 2Gb cartridges appear similar, but there is actually a subtle difference in their shape which prevents a 2Gb cartridge from being fully inserted into a 1Gb drive. Obviously, this means that you can't use a 2Gb cartridge in a 1Gb drive.
The 2-Gb capacity Jaz drives can read, write, and format both 2-Gb and 1-Gb Jaz cartridges.
Iomega markets a SCSI host adapter under the name Jaz Jet. However, there are at least two different SCSI chipsets that are used. For this reason, the Jaz Jet isn't necessarily the best SCSI adapter to buy if you need one for your Jaz drive. You're better off getting a card that you know your Linux distribution will support (see the next section).
One of the Jaz Jet cards is based on the Adaptec 7800 family of adapters. Linux 2.0 supports this adapter with the aic7xxx driver. This driver is built into most of the standard 2.x SCSI-capable kernels supplied with most Linux distributions.
The other adapter is based on the Advanced Systems chipset. At boot time the board gives a message like:
Jaz Jet PCI SCSI adapter Copyright Advanced Systems 1996
Depending on your Linux distribution, you may need to build a custom kernel (with the CONFIG_SCSI_ADVANSYS variable set) to use this adapter.
Personally, I don't like surprises, so if I were going to buy an adapter card, I would get a name-brand card with a 50-pin connector, so that I knew that what I was getting was supported.
If you're using an Ultra-Wide SCSI card with a 68-pin connector, you'll need to get an adapter or another cable. The adapters do indeed work just fine with the Jaz drive, but can be rather pricey, so if you're buying a SCSI card primarily for the purpose of connecting the Jaz drive, you're better off picking up a card with a 50pin connector on it.
If you're looking for a suggestion, I like the Adaptec AHA-2930U - it's cheap, it's fast, and the Jaz drive just plugs right in using the supplied cable with no adapter hassles. Unfortunately, support for this card is fairly new, so unless you have a fairly new Linux distribution (2.2.x kernel), it probably isn't supported. There are patches to the aic7xxx driver for 2.0.36 kernels that support this card, however. The AHA-2940U is an excellent choice as well, and it has been supported for a lot longer, it's just more expensive.
As always, be sure that your Linux distribution supports a particular card EXPLICITLY before making a purchase. Many manufacturers, like Adaptec, have cards with numbers and letters similar to each other that are actually completely different chipsets, and therefore use completely different drivers.
Configuring the Linux kernel for a SCSI card is the subject of a complete document in itself, so I won't go into that here.
Info on rebuilding the kernel should be found in /usr/src/linux/README, or in /usr/src/linux/Documentation/ directory for the 2.x kernels. If these files don't exist, make sure that you have installed the kernel package source for your distribution.
You can also check out Brian Ward's Kernel-HOWTO