[Scst-devel] About IBM iSeries|AS/400 support

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Hello,

I'm a collector (and, in a way, fanboy) of older IBM AS/400, and iSeries hardware, for their quite distinct hard- and software features. I'm a Mac user for decades, so I'm somewhat fluent about SCSI on a higher level, but my skills aren't really solid.

For some time now, I have searched for possibilities to substitute the aging and sometimes power-hungry disk drives with something newer and less expensive (in terms of power dissipation). I was thinking about a PC with a SCSI HBA, connected to the SCSI bus of such a machine, emulating a number of virtual targets backed by files in a(ny) Linux file system. Or, if high performance is a must, tie multiple SCSI buses of both machines together. From an initial glance over the documentation in the source's www subdirectory, this should be possible to do. Is this correct?

After looking at low-end OpenSource possibilities like SCSI2CF, or RaSCSI, I quickly decided that the I/O rate demands of OS/400 might be seriously thwarted by those. Especially considering that these implement 8-Bit SCSI only.

IBM has implemented some extras for different reasons:
- Unusual Disk Sector Size (520, and 522 Bytes),
- Additional SKIP READ and SKIP WRITE SCSI Commands,
- Correct FORMAT UNIT behavior, including a change in sector size during formatting,
- Some "Special" VPD entries, needs to be configurable.

Details as far as I know about them can be read here: http://qseco.fr/research/demystifying-as400-dasd/

I have read that SCST supports some multiples of 256 Bytes per sector, which isn't exactly what IBM uses on disk. However, I think that additional SCSI commands might be comparatively easy to implement. I have not yet looked in great detail at the code base, though.

Q: Could SCST be expanded with moderate effort to support AS/400's as an initiator system, given the available information is complete?

Any thoughts on this?

I'm not very good in programming, but I'm willing to help in any other way possible. Testing, bug reports, and even remote access for first-hand debugging is possible. I do own an 8-Bit SCSI Analyzer, see https://leela.pocnet.net/~poc/DSC-202.mov This means, I can do traces on an older AS/400 with 8-Bit SCSI. But I'll most likely need some advice what exactly is needed.

Thanks for your answers!

:wq! PoC