RE: stat(), st_size and st_allocsize -- MIDRANGE-L

Scott:

No clear disagreement. Any comments about /QNTC are purely from the iSeries 
perspective simply because that's the route my programming must take to reach 
Win2K when the directory path points that way.

Though, even so, /QNTC (or Windows networking support or whatever all gets 
involved) might make a difference. I have no good way to know what _really_ 
happens with internal buffers, data blocks, etc., when I O_APPEND at intervals 
between opens/closes. E.g., is the last block (cluster, whatever) physically 
retrieved from the Win2K Server and brought back to a buffer space in the 
iSeries and then a pointer to the last physical data position found before my 
first write()? or does my program simply start filling a buffer/block and the 
buffer/block is sent all at once over to Win2K when it fills? or is each 
separate write() transmitted? And is it all appended immediately after the last 
physical byte or is it appended by block (cluster)? And when my /QNTC path 
actually points to NetServer on a different iSeries system, does it behave the 
same as Win2K? (Hmmm...)

Lots of possibilities. For my purposes, I don't care beyond simple technical 
curiosity. Just recognizing the real importance of st_allocsize is plenty for 
me.

Thanks much.

Tom Liotta

midrange-l-request@midrange.com wrote:

>  11. RE: stat(), st_size and st_allocsize (Scott Klement)
>
>I wouldn't blame QNTC, but rather I'd blame the way DOS/Windows looks at
>disks.
>
<snip>
>
>My guess is that the 68k cluster size you're seeing is just what Windows
>is using, and is not QNTC's fault...
>
>
>On Fri, 11 Oct 2002, Tom Liotta wrote:
>>
>> Your explanation matches with what I came up with as a working
>> assumption, so I'll go with it.
>>
>> Two items come to mind: (1) A process that attempts to find how much
>> space is being used overall should use st_allocsize rather than st_size.
>> And (2) writes through /QNTC to a Win2K Server can result in very
>> inefficient use of Win2K disk space.
>>
>> I ran various tests to Win2K and continually saw st_allocsize rapidly
>> exceeding st_size as the file grew. Just from the single example I
>> provided, you can see st_allocsize is almost seven times st_size. When I
>> was trying closes and re-opens with O_APPEND, the size difference was
>> worse. Wish I had time for a decent benchmark series.

--
Tom Liotta
The PowerTech Group, Inc.
19426 68th Avenue South
Kent, WA 98032
Phone  253-872-7788 x313
Fax    253-872-7904
http://www.powertechgroup.com


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