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When rust stops spinning – Replacing vintage SCSI harddisks

The other day, the SCSI harddisk in the IBM PS/2 P75 failed – just after I had done a fresh install of PCDOS, Windows 3.11 and OS/2 Warp.

I should have been warned – it made unhealthy noises during the OS/2 install but it went through and worked fine for the day. When I powered the box up a few days later, the disk sounded like the spindle motor was cutting-out and the seeking sound was different than before.

It showed more and more read-errors and in the end failed to boot up anything. The failing drive is a Quantum Lightning 700MB narrow, single ended SCSI-2 disk which I had swapped in replacing the super noisy IBM 0661 Type 467 400MB harddisk.

Quantum Lightning 700MB SCSI, 1994
IBM 0661 Type 467 400MB SCSI, 1992

This particular IBM PS/2 requires SCSI disks with 1024 MB or less capacity, anything bigger causes issues. SCSI drives of this size in good shape are really hard to come by nowadays and if they show up on ebay, asking prices are crazy high and/or the drives are heavily used and sold „as-is“ (as was the Quantum Lightning…).

SCSI Emulation

Today we have SD cards and USB sticks that can store 40 times and more data than the IBM 0661 and there are products out there making them compatible with old-school SCSI hosts. I had this in mind for quite a while and looking back, I should have done it earlier instead of replacing one noisy harddisk with another one.

Originally coming from the Apple Mac / Amiga scene, products like SCSI2SD, BlueSCSI and RASCSI are geared towards replacing 50pin SCSI drives which is what we have in this IBM PS/2 machine too. For anything newer, wider, faster these solutions will be too slow though, however for upgrading a fast, wide drive in a SGI Octane there are other options anyway.

BlueSCSI

I have a spare BlueSCSI device around which I used via a 34->50pin adapter in the Macintosh Portable until I replaced it with one made specifically for this machine, so I decided it would probably be a good fit for the IBM and gave it a try.

BlueSCSI v1.0 with 3D printed adapter frame

Generally, the BlueSCSI is a nice, fool proof device – load it with disk images following a certain naming convention and you should be fine.

Not so in the IBM PS/2 – while it sees the drive presented as SCSI ID 0, LUN 0 with 976MB capacity, it also sses an unknown device on each of the other six LUNs. Since there were no disk images for LUNs other than 0, the IBM wouldn’t know what to do with them an err out.

IBM bootup error codes indicating unrecognized devices on SCSI ID 0, LUNs 1 … 7

Skipping the error with F1 let me boot DOS from a floppy-disk only to discover that FDISK would crash when trying to access the SCSI disk. Adding more disk images didn’t help either because this BlueSCSIs firmware doesn’t accept more than one additional LUN per ID, so still six of them showing up as unrecognized.

I guess this could be fixed with a firmware patch for the BlueSCSI, however reprogramming it requires some special tools that I don’t have, so it will wait for a use in another computer.

SCSI2SD

Since the BlueSCSI plan didn’t work, I took a SCSI2SD v5.1 from my HP 9000/712 computer. My plan was to try it out in the PS/2 and, if working replacing it with the BlueSCSI. Spoiler: the HP 9000 doesn’t like the BlueSCSI either, it sees a drive but refuses to boot from it.

The SCSI2SD works well with the IBM PS/2 SCSI adapter, only caveat is that drives need to be less than 1GB in size to work which is a limitation of the PS/2s SCSI firmware. The SCSI2SD allows to define up to four targets which can be either hard-disk or CD ROM images, so I ended up in creating 4 x 967MB disk images on the SD card.

IBM treats SCSI devices from high to low ID numbers, so the CD-ROM drive shows up first after the adapter as ID 6. I had numbered the virtual hard-disks from 1 .. 4 so ID 4 is found next. Drive letters will be assigned in descending ID order, so ID 4 will be the C drive, ID 3 is D and so forth.

My plan is to install OS/2 with its bootmanager on the C drive and use it to multiboot into OS/2, DOS and other systems.

SCSI2SD devices showing up on the IBM configuration screen

Sidenote on the SCSI2SD: it is somewhat complicated to configure since a) it requires an extra tool for setup and b) it does not work with files but with the start and end block addresses on the SD card that one needs to find out and plug into the config tool. Writing data to the SD card to exact block addresses is somewhat inconvenient as well since it involves several steps to in the end dd a raw file of certain length to a certain spot on the card.

Since I want a easy way to access the drive images individually on another system, I put together a little tool that will find the addresses of disk image files on the SD card and generate a scsi2sd-config.xml file which can be imported straight into the configuration utility.

Once I got the SCSI2SD to work, I needed to think about how to add it to the computer so that I can access the SD card from the outside. I found a MCA bracket on thingiverse that I 3d printed and with that could install it one free of the lower Microchannel slots. The SCSI2SD is powered from the SCSI bus and the internal wiring is long enough for a comfortable fit.

SCSI2SD installed in MCA slot #3

I decided to install the IBM 0661 drive in the drive bay lower right in the back of the computer, completing its original setup. The drive is left unconnected and thus noiseless 🙂

IBM 0661 in its original spot

Speaking of noise – all that’s audible now is the PSU fan which I had replaced with a Noctua NF-A9. It’s not totally silent but has a nice, monotonous, low pitch sound – as opposed to the IBM 0661 and the Quantum Lightning. Either of them made a screaming, saw like sounds – probably due to worn out bearings along with heavy rattling head seek sounds, making the computer unpleasant to use for a longer time.

In conclusion, I’d recommend the SCSI2SD upgrade over real „Spinning Rust“ and over the BlueSCSI that the PS/2 and the HP9000 hated. Should have done it earlier though 🙂

Below is a view into the back of the IBM PS/2 P75 as it stands now, pretty packed. Maybe one more Microchannel card will fit… thinking of a XGA-2 maybe 🙂

IBM PS/2 P75 back view – quite busy inside

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