[OpenAFS] Network becomes terribly slow when cache manager flushes updates over xDSL

Jeffrey Altman jaltman@secure-endpoints.com
Tue, 07 Jul 2009 09:18:14 -0400


Sure it is.  In fact I build OpenAFS within AFS across my NAT'd cable
modem connection while using that connection for many other things
at the same time.  I regularly access AFS using my cell phone data
connection which is sometimes shared by multiple computers by turning it
into a wifi access point.   When you push more data into the pipe than
can squeeze through the pipe at any one time everything will go slower.
If there is significant packet loss on the connection, it will go slower

AFS is a network file system.  It supports local caching.  The caching
is only useful in reducing network traffic if:

 (a) the cache is larger than the working set size of the files
     being used so that thrashing does not occur

 (b) the operations being performed are mostly reads

Programs such as firefox that are performing large numbers of network
operations of their own are going to be competing with the file system
for the same resources.  Firefox in fact is going to be performing a
write to its web cache for every read from a web server.   Storing
such temporary data in network storage over a constrained pipe is not
going to work well.  You should configure firefox to always use
temporary local disk space for its cache.

Jeffrey Altman

Goulou wrote:
> Nobody has any idea about this? Isn't AFS designed to be used over "normal" internet links? Or am I the only one with this slowing-down problem?
> I'll be really happy if anybody would help me...
> Frédéric Grelot.
> ----- "Goulou" <fredericg_99@yahoo.fr> a écrit :
>> Hi all, 
>> I'm trying to give my users an access to their home directory over the
>> Internet, so they can connect to there account from their homes
>> (place, not directory...).
>> Unfortunately, my tests show that when a large update occurs to the
>> disk (for example, the user download a file and puts it in any
>> directory, or makes a copy from USB to home dir), the connection
>> always becomes terribly slow (ping>1000ms), and any other request
>> takes ages to return (thus, if the user uses firefox for example,
>> since it makes quite a lot of disk access to the ".mozilla" directory,
>> its interface freezes until the update if over and ping becomes normal
>> again, i.e 60ms)
>> I managed to optimize this by setting a chunksize of 8kb (smaller
>> seems to fail, because my cache is between about 500Mo-2Go, and that
>> makes too many files for the cachemanager I think), and by adding an
>> "fs st -allfiles 20000" in afs.conf like this:
>> afs_server_prefs() { fs storebehind -allfiles 20000 }
>> It is slighly better with these settings : I still get ping >1000ms,
>> but less often...
>> Is there any ways to enhance this again, or should I set some QoS on
>> the system to prevent afs daemon to send to many packets at the same
>> time (a solution that I'd rather avoid, since I'll not have full
>> control over the client's systems...)?
>> Tanks a lot for your advices!
>> Frédéric.
>> _______________________________________________
>> OpenAFS-info mailing list
>> OpenAFS-info@openafs.org
>> https://lists.openafs.org/mailman/listinfo/openafs-info
> _______________________________________________
> OpenAFS-info mailing list
> OpenAFS-info@openafs.org
> https://lists.openafs.org/mailman/listinfo/openafs-info