[Performance] Samba 3 vs. Samba 4 performance in NetBench

[Andrew Tridgell]

Jeremy,

 > Well the default on NTFS is non-sparse, and you have to explicitly
 > set a file sparse to select that, so I'm guessing that netbench
 > is just doing a good simulation of what Word actually does - ie. it
 > always does the one-byte allocation write.

This might be right, but I have reasons to suspect it isn't.

First off, as files on windows servers are by default non-sparse, the
application would only need to do 1 write at the desired size, not a
write per 2k of file, amounting to hundreds of extra operations. Doing
all those 1 byte writes would only make sense if the application knew
that the server is using sparse files. I don't see any IOCTL calls in
the sniff, so the application is not asking for sparse files, which
means it should be working on the assumption that the files are
non-sparse.

Secondly, the detailed stats in the spreadsheet Marc sent me don't
show a difference in the number of writes between Samba3 and Samba4,
which means at the level that NetBench is measuring the operations
these massive numbers of small writes are not visible. That implies
that the writes are being done at the redirector level, not at the
application level (as we know NetBench measures the operations it asks
for, not the operations actually sent).

The key will be to see if NetBench does these silly 1 byte writes when
talking to a w2k3 server. If it does, then its just stupid
application/redirector code. If it doesn't then we need to know what
factor the client is using to detect that the writes are not needed.

Cheers, Tridge