We are all aware of the infamous 3.94GB IML drive limit on IML based systems. In short, a 4GB drive will freak out an IML based system because of the calculations used to create the 3 or so MB track at the end of the disk  Peter mentions it HERE .

  BUT... after drinking lots of coffee and some empirical evidence from a DDRS-34560 with a T4 and a Corvette in a 9590, I was freed from my primitive understanding of the IML / reference / system partition. Put down the dead chickens and the torches, here's the future. 

SCSI Oddity 2003 (sounds of the fanfare for the common man)

  The flash based systems do not need any reference (or system) partition to boot from. So if you have a 4.5GB DDRS on an enhanced SCSI adapter, in a system with enhanced SCSI support in the bios, then when the SCSI adapter lays the convenience partition in a place >3.94GB, the system can access it and run systems programs. I've done it with a 4.5GB drive.

But, you may wonder, how far can I go and not burst out of normal SCSI space? (Warp 10...)

Cheetah Max Drive Size
John Mes (from that little band down in Texas) wrote:
 These tests are all on a 95A planar, FRU 92F2623, BIOS 08 w/P-90  "Cubrun" complex.

Cards in system:
Slot 1: Cheetah, BIOS 2.14
Slot 2: Corvette, unknown FW rev.
Slot 5: XGA-2

Hard disks:
2x 250Gb Maxtor high-perf. drives w/Acard FW SCSI-IDE interposer 1x IBM DFHS 1Gb

Notes:  The 95A is not an IML system, so a Ref partition is not necessary (at least in this case), just convenient.

Config 1:
  * No Corvette
  * On Cheetah:
    1Gb drive as Array A, Logical Drive 0
    250 Gb drives as Array B, 2Gb Logical Drive 0, 32Gb Log. Drives 1-6
Config 2:
  * No Corvette
  * On Cheetah:
    250Gb drives as Array A, 8x32Gb Logical Drives
Config 3:
  * On Cheetah:
    250Gb drives as Array A, 8x32Gb Logical Drives
  * On Corvette:
    1Gb drive as ID 6
Config 4:
  * On Cheetah:
    -nothing-
  * On Corvette:
    1Gb drive as ID 6
    250Gb drives as ID 5 & 4
Config 5:
  * No Cheetah
  * Corvette in Slot 1
    250Gb drives as ID 6 & 5

Config 1 Results:
  - Ref partition not possible.  System errors with "This system does not support a convenience partition." when booting from disk & trying to create one.
  - All drives format as expected in Fat32 or NTFS
  - OSes boot as expected (see OS Notes)

Config 2:
  - Ref partition not possible.  System errors with "This system does not support a convenience partition." when booting from disk & trying to create one.
  - Drives format as expected in Fat32 or NTFS
  - OSes boot as expected (see OS Notes)

Config 3:
  - System will allow the creation of an IML track on the 1Gb disk
  - Everything else goes like before

Config 4:
  - IML track will only go on 1Gb drive, no matter what.  This is, I'm sure, due to the physical constraints noted on Peter's site of which we're all familiar with. ;-)
  - 250Gb drives show up as -30Gb drives, but will partition & format 
under Fat32 and NTFS up to capacity without any trouble

Config 5:
  - System stays in a error 206701 error loop.  No drives show up at all on the Corvette.

Conclusions:
- The Cheetah can handle really big drives and report their size correctly; but past 200Gb, you're wasting space since there's the 8x32Gb logical drive limit.  Back in the day that (32Gb) probably seemed more like a theoretical limit, but here we are.
- The Corvette will handle big drives as well, but only if there is a conventional (<8Gb - see Peter's site again ref big drives and IML) drive present.  I'm sure this has to do with an addressing limitation (23 bits overflowed to 24 on 250Gb would explain the -30Gb size) and perhaps an Int13 hook limitation.
- The system is QUIET with all IDE drives!  Wow!  Talk about impressive. IDE has come a long way, and the MTBF on these Maxtors is >1M hours, which is right up there with SCSI devices.  I think maybe a small IDE device on the Corvette could be the IML & booter..... eh, some other time.

OS Notes:
- Windows NT4, IIRC, requires that its boot partition reside within the first 1024 cylinders of the hard disk.  Maybe PowerQuest found a way around that, I don't know.
- Netware (all versions) boots from a DOS partition, and so all DOS limitations apply.  However, it can load postively huge (up to 32Tb and beyond on newer versions) drives as its main partition.
- Win95OSR2 and Win98 seem to have DOS limitations on booting, but don't have any trouble ignoring the 1Gb drive and booting from 120Gb.
- All OSes worked fine when the 1Gb drive was left unpartitioned (as IML only).  NT Disk Manager complained a bit but worked anyway.

   This IDE-to-SCSI converter is poodle faking anyway. It wouldn't surprise me a lot, when it turns out later, that the converter cannot handle the logical blocks calculation properly and returns false values to the Corvette, when it sends a "show device size" command. But even the most advanced SCSI command set (of 1992 or around) must have a natural limit somewhere .... ;-)