Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcdc!hpfcmgw!rocky
From: rocky@hpfcmgw.HP.COM (Rocky Craig)
Newsgroups: comp.sys.hp
Subject: Re: Diskless environment, what kinda kernel on the server ??
Message-ID: <1080064@hpfcmgw.HP.COM>
Date: 6 Jul 89 17:00:54 GMT
References: <1428@ruuinf.cs.ruu.nl>
Organization: HP Fort Collins, CO
Lines: 66

> Well, if anyone has experimented with tunable kernel like "dskless_*", "nbuf"
> and "netmem*" parameters in an environment like the one described above or

I'll do the easy ones first :-)   The netmem* parameters are for IP connections
(and other things) in our ARPA product.  The diskless message protocol does
not use those buffers, so changing them will not affect DISKLESS performance
(file system and remote swap).  Your overall system performance could 
change depending on the number of "normal" network connections you establish
(Telnet, rlogin, etc.)

HP's diskless has a "dual-cache" scheme for file system access.  There
is a buffer pool on each diskless node.  When a buffer needs to be flushed,
it will go to a (shared) buffer pool on the server.  The server will then
manage the asynchronous disk access, deciding when to actually write the
data to disk.  Various synchronization checks exist to guarantee expected
UNIX* operation (mulitple writers, distributed FIFOs, etc.); HP-UX diskless
passes the SVVS!

The network buffers used for remote filesystem access are taken as a
subset of the overall file system cache.  To improve file system performance,
you want to maximize the size of the shared cache on the server.  The size
of the cache is controlled by nbuf.  On your 16 megabyte system, this number 
will default to 268 pages (one page = 4k bytes), or a little over one megabyte.
If you are using the server in a dedicated fashion and can spare the extra 
memory, bump nbuf up to its maximum of 768 (three megabytes).  Be careful 
about changing nbuf on diskless nodes.  You might try it, but it will 
definitely take some experimentation to find the right value.

The other "diskless" parameters you mentioned are all calculated (by default) 
based mainly on the parameter "num_cnodes".  This is not a limiting
parameter, but a guestimate as to the average number of cnodes this
server should be expected to support.  It defines other parameters and the
size of various tables and buffer pools.  In your case, I would suggest 
setting it to 25 (or maybe even 30).  The only "cost" is server memory 
(of which you have plenty on your dedicated server).  It's doubtful that 
changing the individual parameters (instead of relying on their value 
obtained from num_cnodes) will get you anything extra.

The main performance bottleneck in diskless clusters occurs when diskless
nodes start paging (remotely).  Do everything to maximize available memory
on those nodes: remove unneeded drivers from the kernel (fpa, nfs if you
don't need it, etc.), don't run superfluous processes (netlogstart, vtdaemon, 
rwhod are good examples).  Your server will still have quite a bit of
available memory; if it makes sense, you might want to run some of the
X11 clients on the server.

Naturally, in the benchmarking/performance tuning world, the final answer
is always "That's too vague to answer definitively", or the simpler,
"That depends" :-)  Your mileage will vary, but this should be a good start.
Most of this information is contained in the System Administrator manual.
Some pieces are in the networking manuals.

Good Luck!

Rocky Craig			
Hewlett-Packard Workstation Group, Marketing Event Technical Support
3404 E. Harmony Road, Ft. Collins, Colorado 80525-9599

Internet:	rocky%hpfcmr@hplabs.hp.com
UUCP:		...!{hplabs | hpu*}!hpfcmr!rocky

This article does not represent the official position of the Hewlett-Packard 
Company.  The above data is provided for informational purposes only.  It is 
supplied without warranty of any kind.

* UNIX is a trademark of AT&T in the U.S. and other countries