<snip/>
> Right now, BIO_MAX_SECTORS is only 64k, and IDE can
> take twice that. I'm not sure what the largest
> request size is for SCSI - certainly 128k.
Scatter gather lists in the scsi subsystem have a max
length of 255. The actual maximum size is dictated by
the HBA driver (sg_tablesize). The HBA driver can
further throttle the size of a single transfer with
max_sectors.
Experiments with raw IO (both in 2.4 and 2.5) indicate
that pages are not contiguous when the scatter gather
list is built. On i386 this limits the maximum transfer
size of a single scsi command to just less than 1 MB.
Doug Gilbert
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