Re: scsipi: physio split the request

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Dec 27,  6:49pm, Michael van Elst wrote:
} manu%netbsd.org@localhost (Emmanuel Dreyfus) writes:
} 
} >Is there a reason other than historical for NetBSD 64kB limit?
} 
} It's a compromise. Some buffers are statically sized for MAXPHYS
} and some ancient hardware cannot exceed 64k (or even less) DMA transfers.
} The buffer size is mostly a problem because we don't support
} scatter-gather transfers, so the buffers need to be contigous in
} physical RAM (and some hardware doesn't support s-g either).
} 
} So far that's mostly a problem with software raid and modern tape I/O.

     Wouldn't hardware RAID also benefit from bigger buffers?
Although, I suppose a battery backed cache be used to workaround
small transfer sizes.

}-- End of excerpt from Michael van Elst