[rescue] CDROM 512-byte boot questions

[vom513]

> On Jul 27, 2023, at 12:54 PM, Jonathan Sturges via rescue <rescue at sunhelp.org> wrote:
> 
> Hi,
> Nice summary, your understanding is correct.  Some small additions:
> 
> *  Some OSes -- Solaris2, I'm fairly sure, maybe later SunOS? -- the SCSI drivers can issue the block size change command when the OS is running (or are able to handle the 2k block size).
> *  OBP 3.x can issue the block change command too, IIRC; it's really OPB 2.x and prior that have the hard requirement of a 512-byte block requirement for booting.
> *  Besides Plextor, most Panasonic, Toshiba and Pioneer drives have jumperable block sizes.

Thanks for the reply/confirmation.

I did a bit more experimentation with the ZuluSCI and figured I’d post my results to the list to benefit any future folks who might be looking for this type of info.

- CD6.iso : Zulu log shows it coming up in 2048-byte mode, but my sun4c/m machines boot fine from it.  I don’t see a MODE SELECT in the log - I guess the ZS is just operating in “soft” block mode and honoring whatever request comes in ? (This is great by the way - not looking a gift horse in the mouth)

- CD6_512.iso : Block size specified as 512.  Works as expected.

- CD6_2048.iso : Block size specified as 2048.  Machines will NOT boot.  

So it seems like _<BLOCKSIZE> is a “hard” setting.  Omitting this seems to run the device in “soft” mode (hard/soft just my personal terminology for this behavior).