> One thing that confused Tru64 Unix a while back was Sun clients writing
> to Tru64 servers. We only support 8KB (or less) I/O sizes, and the Sun
> clients really wanted to do 32 KB. So, we'd see the first 8 KB of many
> 32 KB chunks, then the 2nd 8 KB, then 3rd, then 4th. Then the pattern
> would repeat with the next set of I/Os.
>
> One (or both?) of our physical file systems saw this pattern and wrongly
> concluded that the client was doing random access I/O, and that lead to
> inefficient block allocation. If Linux clients do read ahead, that
> might be confusing Solaris. Perhaps the 4 KB I/O size doesn't trigger
> readahead. Hmm. If you read a file that you just created on Solaris,
> I'd expect that to be in Solaris's cache and it shouldn't need to read
> from the disk anyway.
The latter is indeed quite puzzling, but the difference between the
read/write speed to ramdisk and the read/write speed to harddrive
indicate that the server-side caching is somehow failing. A tcpdump
would indeed help in debugging this.
Anyhow, implementing support for 32k rsizes didn't turn out to require
much extra code, so I wrote it last night.
Cheers,
Trond
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