[OpenAFS] Re: File server memory requirements

Andrew Deason adeason@sinenomine.net
Sun, 19 Jun 2011 18:59:53 -0500

On Mon, 20 Jun 2011 00:38:47 +0200
Jaap Winius <jwinius@umrk.nl> wrote:

> But, to see if I this is necessary, how can I tell what the (maximum)
> number of callbacks is that my fileserver is actually setting?

This command will give you some callback-related information:

xstat_fs_test <fileserver> -collID 3 -onceonly

The information it gives you is briefly described here:

The -cb option in the fileserver sets the number of FE and CB entries
that are allocated. If the nFEs or nCBs fields in the xstat_fs_test
output ever is about to exceed that number, the fileserver reclaims
callback space and it results in bad performance (and in older versions,
bad stability). Every time that happens, the GetSomeSpaces counter is
incremented, so if it's 0, you have nothing to worry about.

We don't currently give a statistic for the highest number of callbacks
utilized (although that would be useful); the nFEs and nCBs fields only
report the current utilization. You can roughly figure out what the max
is, though, if you query xstat_fs_test a lot over time.

If you don't actually need more than 64 thousand callbacks, increasing
-cb isn't going to help you at all for performance, and is going to take
up memory that could otherwise be used for filesystem caches for the
local disk data.

Andrew Deason