SCSI drives up to 2 GB should work great. However, larger capacities aren't supported by all OS versions and machines, but you can always partition a big disk in several chunks just below 2 GB...
A few points to consider, just in case:
•Some drives (esp. server ones) can draw a lot of power, while the IIsi PSU is somewhat limited... check the amps needed for the +5 and +12 rails of the drive before purchasing -- it's indeed related to heat generation, something you want to be controlled inside a plastic IIsi... But, up to 2 GB this isn't likely to be an issue.
•For a Macintosh, best are 50-pin drives, but they're becoming somewhat rare. It's possible to use 68-pin and 80-pin (SCA) drives with a suitable adapter. With these wide-SCSI drives, sometimes you'll need to tinker with jumper settings in order to enable 8-bit (narrow) transfers, and/or disable the delayed startup. Some Ultra-320 drives do not support narrow transfers at all. But once again, this is more for larger disks.
•Unless you're lucky enough to find an Apple branded suitable drive, regular Apple formatting utilities will refuse to work on your disk... Use a third party formatter, or the patched version of HD SC Setup / Drive Setup.
A few points to consider, just in case:
•Some drives (esp. server ones) can draw a lot of power, while the IIsi PSU is somewhat limited... check the amps needed for the +5 and +12 rails of the drive before purchasing -- it's indeed related to heat generation, something you want to be controlled inside a plastic IIsi... But, up to 2 GB this isn't likely to be an issue.
•For a Macintosh, best are 50-pin drives, but they're becoming somewhat rare. It's possible to use 68-pin and 80-pin (SCA) drives with a suitable adapter. With these wide-SCSI drives, sometimes you'll need to tinker with jumper settings in order to enable 8-bit (narrow) transfers, and/or disable the delayed startup. Some Ultra-320 drives do not support narrow transfers at all. But once again, this is more for larger disks.
•Unless you're lucky enough to find an Apple branded suitable drive, regular Apple formatting utilities will refuse to work on your disk... Use a third party formatter, or the patched version of HD SC Setup / Drive Setup.