Please do not reference Indigo with Indigo2 systems interchangeably, they are completely different systems, shorthand will only lead to troubles. You asked about an Indigo2, these statements apply to an Indigo2.
OK, I'm hoping this was just a misunderstanding:
http://sgidepot.co.uk/cdtips.html
I only use Toshiba SCSI DVD drives, I don't own a single toshiba CDROM drive, all of my SCSI CDROMs are SUN rebranded caddy-loading models because those "just work".
To boot SCSI SGIs, you must either MANUALLY (or have CDROM firmware custom defaulted ...like some drives sold with SUN stations) enable 512 Byte Block mode on optical drives to even recognize the media as..well media. It doesn't matter if it can do it in software with a SCSI command...you won't get that opportunity during OS install. It must work from the first command to load the SASH.ARCs or the miniroot from the CDROMs, there isn't anything before that on OS install from bare metal. Because that's how SGI sold their systems. Also some of these drives have different firmware defaults, for UNIX stations sold with drives, this was done. In PC land...no it will first advertise 2048. I've heard people claim certain PROM versions of Indigo2 can software-switch block size modes...I've never witnessed this working on any SGI. It's a statement someone made, I cannot confirm it, so I don't.
The SCSI bus will absolutely be reset on reboot on an Indigo2 (SGIs love to reset buses...it gets bad sometimes), so I doubt you can issue the command, then preserve the drive state through reboot., it's also highly likely that once the OS loaded from CD, the kernel driver will reset the devices anyway and then the rest of the CDs wouldn't work. I don't know who gave you info that they don't reset...yeah they do...a lot, if something isn't right or they just get a response they don't understand or just because they want to.
On any SCSI system, all SCSI devices must agree on certain settings, parity is one of them. Either EVERYTHING is parity or nothing is parity, so if you just tried setting one device as parity ON and another drive was installed as OFF...yeah you'd have problems. SGIs can work in either way, but the preferred settings recommend by the SGI manual is PARITY ON because it validates all data pulled from media to protect/detect against data corruption on the bus and device caches.
I never said you had to use 1,2,3 (I said you could stay @ ID 6). I just said that the sled's auto-numbering functions (if you hacked them to use them without the official cables) and the documentation (and convention) is to number them in the way I suggested. It's your choice (as I mentioned), however statements in the manuals assume SCSI ID 1 is the booting drive and ID 3 is CDROM, so when following directions you'll need to change what you type. I recommend you go with the convention to make things easier on you.
You absolutely cannot use SCSI ID 0 for anything, that ID is hard-set by the system controller's use and cannot be changed. PC's normally used 7 for higher priority, it is unknown why SGI choose the lowest priority ID of 0 for it's controller.
NEED -> 