[OpenAFS] appropriate -cb numbers for fileservers?

[Mark Vitale]

> On 8 Sep 2022, at 10:00 AM, Dave Botsch <botsch@cnf.cornell.edu> wrote:
>=20
> What's the best way to determine appropriate -cb numbers for
> fileservers? And is there a max that is "bad" like with -p ?

Start with checking your current callback stats:

18:12:16 mvs1:sna-openafs-master mvitale$ xstat_fs_test mvs1 -onceonly -col=
lID 3

Starting up the xstat_fs service, no debugging, one-shot operation

------------------------------------------------------------
                34 DeleteFiles
                 0 DeleteCallBacks
               870 BreakCallBacks
               480 AddCallBack
                 0 GotSomeSpaces
                 3 DeleteAllCallBacks
                 0 nFEs
                 0 nCBs
             60000 nblks
                 8 CBsTimedOut
                 0 nbreakers
                 0 GSS1
                 0 GSS2
                 0 GSS3
                 0 GSS4
                 0 GSS5

The 'nblks' value is identical to the -cb value being used by the fileserve=
r.
The 'nFEs' and 'nCBs' values should stay _well_ below 'nblks'.
So the best way to ensure that is to monitor these values periodically and
keep the data in a time-series database so you can chart them as needed.

Whenever either nFEs or nCBs exceeds nblks, you will see the=20
'GotSomeSpaces' counter increment.  (The GSS* counters will also increment
in a way that is useful only to developers.)  Even one GotSomeSpaces event
is extremely bad for fileserver performance.

My rule of thumb is that when you see nCBs or nFEs approach 50% of nblks,
it is time to double your current value of the fileserver -cb option.

If you find that callback space is being consumed at an unreasonable rate,
there are additional (but very obscure) ways to identify which client(s)
are responsible for the callback load.  Let me know if you want more=20
details on that.


Hope that helps,
--
Mark Vitale
Sine Nomine Associates