> Is it possible to add a SCSI disk inside a SPARC 10 ?

Yes; I've done it with my SS10.  I don't remember details, though; I
took the disk out quite a while ago because it was running hot enough
to worry me (the outside of the machine's case felt disturbingly warm,
even).

> In general should I have troubles adding SCSI devices to a sparc 10
> ??

I haven't, but I haven't done anything very outré.  I'd _expect_
problems to mostly be OS problems, but you never know.

> There is any PROM limitation about the SCSI disk size allowed ??

Even machines with limitations generally don't have a limitation on the
disk size allowed, but rather on how far into the boot disk the boot
partition can be.  Usually, the actual limit is that all blocks read by
the PROM must be in the first 1G of the disk; unless you really want to
get your hands dirty, this means your boot partition must be entirely
below the 1G mark.

I haven't seen any sign of such a problem on my SS10, and its boot
partition is about 2G.  I suppose I _could_ have just been lucky[%],
but given how many kernels I've test-booted, that seems unlikely.

[%] This is possible; if you write a file on a large partition, the OS
    may choose only blocks early in the partition, in which case it may
    not run into the 1G trouble.

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