[sane-devel] ADF Duplex performance problems

[m. allan noah]

2010/5/3 Simon Matter <simon.matter at invoca.ch>:
>> On Sun, Apr 25, 2010 at 4:45 PM, Ilmārs Poikāns <ilmars at delibero.lv>
>> wrote:
>>> Hi,
>>>
>>> I'm running latest SANE from git source on Ubuntu 9.10. I was testing
>>> scaning A4 on Fujitsu ScanSnap 500 in 300 dpi Color uncompressed using
>>> scanadf. Everything is fine when scanning only one side of sheet (image
>>> size
>>> 24MB). But when scanning with "ADF Duplex" as source, scanner pauses 3
>>> times
>>> during scanning. Two 24MB files are saved successfully. Clearly pausing
>>> is
>>> caused by data transfer issues somewhere.
>>
>> Does this happen on windows?
>>
>>> Any ideas where could be the
>>> bottleneck? Scanner can't send data so fast over USB?
>>
>> Almost certainly.
>>
>>> Buffer too small for
>>> USB transfers, so too many data exchange transactions creates delay and
>>> slowdown of throughput?
>>
>> You can try increasing the buffer-size option in /etc/sane.d/fujitsu.conf.
>>
>
> The config states:
> # to set data buffer size, in bytes
> # the value ranges from 4096 - infinity
> # but you may have scanning problems with
> # a value larger than 65536 (the default)
> option buffer-size 65536
>
> I'm just wondering what kind of scanning problem may I have with bigger
> buffer-size? Does it still apply to version 1.0.21?

This option is in all versions of sane-backends for the past several
years. It won't damage the scanner, but it can refuse to scan, or
cause the scanner to pause, very much like it does when the buffer is
too small. Try it. Unfortunately, I don't feel comfortable increasing
this value across the board, since many older machines (M309*) may not
like anything greater than 64K, and I don't know which ones.

allan
-- 
"The truth is an offense, but not a sin"