During a backup of an HP-UX 11 client to a Solaris 8 server running TSM,
what do these Tivoli parameters really control?

1) "TCPWindowsize"
    Am I correct in assuming that Tivoli uses this value to set SO_SNDBUF &
SO_RCVBUF
    in call to setsockopt? If so, then it controls the TCP window size for
each socket
    connection and overrides the system settings for TCP window size. Of
course, the
    lesser of the client send window & server's receive window settings will
form the high
    water mark for sending TCP packets down this socket. Assuming send &
receive
    buffers are empty, the client can therefore send multiple packets of
data without
    waiting for an acknowledgement - up to the TCP window size.
2) "TXNBytelimit"
    Am I correct in assuming that Tivoli uses this in the write call to the
socket? Of course,
    the write buffer may be constrained to be smaller in certain
circumstances. If this is the
    case, then the write size itself can be less than, equal to or greater
than the TCP
    window size & the call will still work properly.
3) "TCPBuffsize"
    The ADSM documentation says this "specifies the size of internal TCP
communication
    buffer". I don't know what this does at the system level, nor how it
relates to above.
4) "USELARGEBUFFERS"
    For files > 500 KB, larger communication buffers are used. I don't know
what this does
    at the system level, nor how it relates to above either.

As far as I know, the SO_SNDBUF on the sending side, and SO_RCVBUF on the
receiving side, control both the respective send/receive TCP window sizes
and the size of the send/receive TCP buffers. If this is so, then one of
them should be small (maybe 32 or 64 KB) to "fill the pipe" and the other
could be much larger to serve the give one side a larger TCP buffer. In
other words, it seems that there might be some benefit to making the client
TCPWindowsize small (maybe 64 KB) and setting the server (receiving side)
large (maybe 1 MB). I'm thinking that the TSM server would have minimal
latency for reading from the socket because the TCP buffer would likely
always contain some data. Any comments?

Roy J. Martin
EDS - GDS - Data Management Group
mailto:roy.martin AT eds DOT com