Buying a mainframe - peripherals
Finishing the guide on purchasing a mainframe, this article will cover what peripherals you need and where you might source them. This is something you should consider before finalizing your order, however, as these peripherals can significantly affect what you can do with your mainframe.
DASD, or disk storage in the open systems world, is the most important and hardest peripheral to obtain. You will have to worry about two types of DASD when setting up your machine: FBA and CKD. FBA DASD is quite similar to a standard PC disk. It has fixed sector sizes and can be set up using commodity hardware. On any z10 or later mainframe, you can use any traditional fiber channel storage as FBA DASD. Considering standard FC storage is cheap on eBay and easy to DIY, this will generally not be a problem for any prospective mainframe owner.
The primary concern for storage is CKD DASD. CKD storage is required for z/OS and z/TPF, and it cannot be created easily (at least not yet). This difficulty is caused due to the way that CKD storage records block sizes. Essentially, CKD disks report their geometry to the host computer, allowing the user to choose how the block size for each disk that will be defined. Back in the day when this was first invented, this allowed for massive speedups, as programmers could optimize file storage for the disk geometry they would be using. Unfortunately, this added control requires commands that are not native to SCSI. Instead, both ends of the connection must natively support the FICON protocol (or its predecessor, ESCON). This support is only found in official mainframe peripherals, which are usually extremely large and even rarer than the CPUs they attach to. If you are going to purchase a mainframe, proceed under the assumption that you will not be able to get CKD storage. Most people manage to track it down eventually, but it is not guaranteed and may take years.
When looking for CKD/FICON storage, you should generally look for a few models online. The most common is a DS6000 unit, which is the cheapest and easiest to transport. The downside of this, however, is that they have a nasty tendency of breaking and being extremely unreliable. Despite this, they are suitable for most home users, and you should defiantly purchase one if you can. If you need repair advice, this guide is helpful. The next most common units for sale are DS8k models, ranging from the original DS8300 to the most modern DS8900 units. If you have the space and power for any of these, they will almost certainly meet your needs for years to come. The only thing to remember is that spare parts for DS8300s are getting relatively thin on the ground. Finally, the most rare are the third-party storage units made by Hitachi, Infinidat, and Dell EMC. I know very little about Infinidat and EMC units and, therefore, will avoid giving purchasing advice on them. On the other hand, Hitachi VSP units have an excellent reputation and also use standard racks. If you can find one, they are a perfect choice for a homelab.
Tape storage is optional for a mainframe. It is helpful and generally beneficial, but it should be okay if you cannot get it for your machine. If you decide to look for tape, you have a few options. First, there is the physical tape option. This option makes use of a tape drive and a tape controller. The drive is the easier of these elements to acquire. Any drive from the TS1100 and TS1000 family will work, although you should ensure that your drive is older than your controller. If you have the space to spare, a physical tape library like something from StorageTek or a member of the TS4000 series can be fun, but this kind of unit is usually overkill for a hobbyist. Tape drive controllers are power and RS/6000 boxes that run AIX and have either FICON or ESCON cards. Since I have yet to get one of these, I do not know much about them, but like most other peripherals, as long as they have not been wiped, they should be good to go. If you feel like an adventure, you can get one to work by building one out of spare parts and tracking down the software somewhere.
The second option available for tape is a virtual tape library. These devices present tape drives to the mainframe but store data onto a disk. Many of these units can also be used as a controller for physical tape drives. On the IBM side, these are part of the TS7000 family. As with most IBM kit, these units are solid if you can find them, but they are physically large. The most common units you will find are either custom-built or used EMC DLm2000 units. Since these units are x86-64 based and use “standard” FICON/ESCON cards, they can easily be virtualized if you can find the software (ask around in some of the mainframe discords). Many companies have taken a stab at making a virtual tape appliance, however, and you will almost certainly be able to find something online.
Proper channel-attach printers have been obsolete for decades now, to the point that they are no longer made. This is a good thing for hobbyists, as it means you don’t need to buy a massive and proprietary channel attach printer. Any existing IP printer will do. If you want a classic mainframe line printer, the IBM 6400 series units are readily available and will be a good fit for any lab. Connect one to a print server, and enjoy classic green bar sights and sounds. If you already have a large-format capable printer, you can manually separate the green bar paper and load it into the tray. This is a simple and accurate way to emulate some of the giant IBM and Xerox continuous laser units.
On almost all modern machines, terminal access will not be a problem. You can take your pick with access methods. Modern mainframe OSes support telnet and SSH 3270 emulation, and the underlying hardware supports OSA-ICC, which allows you to define one of your copper OSA ports as an integrated telnet console controller for OS installation and maintenance use. If vintage CRT 3270 terminals are more your speed, I highly recommend building an OEC. This open-source implementation of a terminal controller allows you to avoid having to find and upkeep a 3174. Unfortunately, 3174s with intact firmware are getting remarkably difficult to find, and the OEC provides the same functionality without the hassle.
For the physical console, anything that you can find will work perfectly. The communication protocol is the same from the original 3270s to the modern info windows. Any terminal will work with any controller. If the terminal you are looking at has been separated from its keyboard, any set 3 board should work perfectly. I recommend one of the unicomp reproductions (look for the terminal 122-3270 type in the customizer).
The final type of peripheral that I would like to mention would be development emulation devices, like the FlexCUB from FlexES. These devices connect to the mainframe, usually over ESCON, and enable you to emulate any mainframe device, from a card reader to DASD. I can tell you from first-hand experience that having access to one of these devices is nice, and lots of fun (especially if you are interested in recomputing), but they are unfortunately quite expensive and heavily dependent on licensing. If you have the resources, though, I highly recommend one.
If you have been following along at home, you should have: purchased a mainframe, installed it into your house, and found enough peripherals to meet your needs. If this matches your situation: Congratulations! You have now completed the most challenging phase of setting up a mainframe lab for yourself! If you have any trouble along the way, have any questions, or want to talk about mainframe, feel free to email me! I love to see new people get into the mainframe community.