Interesting. Well, the fileserver code is rather behind the cpu code
for this controller. Perhaps jmk's rumoured fileserver hacks to allow
driver sharing will help here.

In the meantime, you may enable diagnostics in scsincr53c8xx.c:

/*******************************/
/* Fileserver specific defines */
/*******************************/
#ifdef FS
#define xalloc(n) ialloc(n, 1)
#define KADDR(a) ((void*)((ulong)(a)|KZERO))

#define KPRINT if(1)print
#define IPRINT if(1)print
#define DEBUG(n) ((n) <= 2)
#define IFLUSH()
#endif

This will produce a lot of output. Perhaps it should be caught
using a uart console....

It will certainly give more clues.