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Subject2.4.17: Hardwired limit of parallel nfs mounts
Date
Hello to everyone,

I have a question regarding the maximal number of NFS-mounts in Kernel 2.4.17
(on a i686 box running suse7.3). I found out that this number is hardwired
in the kernel in linux/fs/super.c in the bitmap unnamed_dev_in_use.
Since we have put all the data of our users (~4000) on several central NFS
servers it happens sometimes that eg. the mailserver (running linux) has to
mount several hundred home directories by autofs e.g. when users are reading
Mail by POP/IMAP. In this sense the limit of 256 is quite small. Even when I
set the expiration time of autofs to a quite small value it happens sometimes
that autfs cannot mount home directories since the mtable is currently full
(errno: EINVAL).

To change the limit I simply replaced the limit of 256 by 1024 in super.c. In
this situation I can mount about 800 NFS-directories at the same time and
then the kernel complains in /var/log/messages:
....
automount[861]: attempting to mount entry /home/anotheruser
Jan 15 09:03:11 bris kernel: RPC: Can't bind to reserved port (98).
Jan 15 09:03:11 bris kernel: NFS: cannot create RPC transport.
Jan 15 09:03:11 bris kernel: nfs warning: mount version older than kernel
Jan 15 09:03:11 bris kernel: RPC: Can't bind to reserved port (98).
Jan 15 09:03:11 bris kernel: NFS: cannot create RPC transport.

Nothing serious happens, exept that I cannot mount more NFS-Dirs until
autofs has expired some of the ones previously mounted.
Does anyone know why this happens? Do I have to change anything else of the
kernel to allow a number of about 1024 NFS-mounts at the same time?

Wouldnt it be generally a good idea to raise this limit or to make the value
configurable in any way? Why does this limit still exist anyway?

Thanks to all
Rainer
--
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Rainer Krienke krienke@uni-koblenz.de
Universitaet Koblenz, http://www.uni-koblenz.de/~krienke
Rechenzentrum, Voice: +49 261 287 - 1312
Rheinau 1, 56075 Koblenz, Germany Fax: +49 261 287 - 1001312
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