Hi Tom,

>>> More tests: http://jafile.com/uploads/dos386/perftest.txt
> unless dos386 describes what program(s) he used on what hardware
> to produce these results, the data are useless :(
>
>> ...you can try first writing some dummy data at where the file
>> will end, then close it and re-open (without truncate of course)
>> and do the actual copy. That should bundle the FAT updates and
>> increase performance significantly :-)
> just did exactly this (for command.com) COPY.
> unfortunately performance remains the same.
>
> for a single drive (that is able to read ~43 MB/sec), using
> a copy buffer of 60K (Freecom default), copy performs
> roughly identical, even if the file is pre-created.

Please explain. You compiled a modified version of the built-in
COPY command of command.com? My suggestion was to pre-grow the
file, not only pre-create it. Something like, ca 2 GB example:

- open and create a new file for writing
- seek to offset ca 2 GB (works even though file is still empty)
- write 1 byte of data at this place
- close the file

(this should allocate all clusters for a full 2 GB file in FAT)

- open file for writing (no truncate)
- file is now 2 GB but data is "random" contents of whatever
  was in the before-unused clusters unless your kernel was
  compiled with WRITEZEROS (normally not the case)
- write 2 GB of normal data to the file in big chunks,
  preferrably with a copy buffer not wrapping a linear 64 kB
  offset and with a size which is a multiple of 1 cluster.

(should only have to write data, FAT unchanged, few seeks,
in particular if FAT data can use BUFFERS or a read cache)

Eric

PS: http://jafile.com/uploads/dos386/perftest.txt says the
test involves R/W of one file of 2'400'000'000 Bytes but it
does not specify which int21 functions or tools were used.


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