settable optimal transfer size for a given cygwin-install, (or just set it to 4MB)

[Linda Walsh]

It may not be optimal for everyone, but for most systems I've seen, increasing the default I/O size to ~ 4MB would seem to provide a big boost in performance both in local file access as well in network file I/O.

Just now I wanted to copy some files from a local disk to my network and ran 'cp'.  I coughed, when I saw only 50MB/s.  I ran a for i in *; dd if/of bs=xx oflag/iflag=direct;done type loop in it's place.  Tried 16MB first and got 98MB throughput -- but trying 1MB->16MB, 4MB seemed to do the best and gave about 105MB/s.  Not bad for unoptimized file transfer.

For optimized file writes (large, linear, defrag'ed files, with target space pre-allocated as well), my max network speed is 125MB/s, and reads @ 109MB/s, so 105MB/s isn't bad.  

If providing some way to set the 'optimal I/O' isn't possible, could this be upped to 4MB in cygwin?  I'd think this would benefit nearly all systems, but obviously I can't bench them, which is why it'd be neat if it could be configured, perhaps with a registry or ENV setting.

I know it was increased once due to complaints about excessive fragmenting (and that helped speed as well), but making it larger would really help speed too.

Thanks & Hoping...
Linda


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