Re: SCSI Driver

[Stephen Usher <Stephen.Usher@earth.ox.ac.uk>]

>=================================================
>A few years ago, I wrote a hard disk driver of my own, called CBHD.
>It has been published as part of a book that I wrote ("Scheibenkleister"),
>together with other hard disk maintenance software. At the time,
>the book and the driver were very successful in Germany.
>=================================================
>
>I'm in favor of this.  Also, we can steal the Linux SCSI driver and some
>of its other things and hack them up (not steal the code - learn from their
>code).  I am not in favor of 64 bit block numbers though.  Most file systems
>are only 16 bit (tosfs and the original minix file system, although I can't
>be sure of MiNT's minixfs or any V2 system) and are limited to 32 or 64MB.
>64 bit would be ... well ... more than enough.   32 bit is a limit of 4GB
>per device.  While I'm sure there are 4GB device around, I think we can
>wait to implement that.   Consider that a 68K can't work with 64 bit numbers.
>Efficiency would be a problem I think!!

Hmm.. I think restricting disk block/sector numbers to 32 bit would be a
grave mistake. There are already 9GB disk boxes out there, 4GB is becoming
commonplace using multi-disk virtual drive technology. OK, they are
currently quite expensive, ie about #1500 stirling for 4GB, but the price is
falling VERY quickly.

As for the filesystems.. The Minix Filesystem is starting to look a little
cramped, but MiNT can use other filesystems such as the new 4.4BSD one (once
someone's written it ;-)) which is full 64bit.

As for efficiency, you can take the 64bit number as being two 32bit numbers,
segment+offset. You only load the segment long word when you get an overflow
from the offset, so most of the time there is no speed difference.

Steve

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