If the drive's capacity is less than a GB, System 7.5 can handle it. There may be other considerations than size. What state is the drive in? Did the drive come from the PC world? What is its recent history? That is:

is it known to be working (even if you are only about to install a same/different System)?

is it recently formatted (with Apple's disk utility, or another)?

is it erased only?

is it terra incognita?

&c., &c.

Do you hear/feel the drive spin up, and do its chk chk chk chrrrk self-test?

The process involves erase (optional), format (obligatory if you have zero-ed the drive completely) and install. If the options exist, is it jumpered for termination, termination power (from itself or from the bus) and SCSI ID. C'mon. 'Fess up. You'll feel so much better ...

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