Summary
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I am currently unable to mount more than 256 NFS filesystems under
Linux. I have tried several ways to get around this, but they have
all failed. After reading up on devfs, I decided to try it. However,
I am still unable to mount any more partitions. Is there any way
devfs can be used to do this?.
Details
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I am currently running Debian GNU/Linux 3.0 (Woody), 2.4.17 kernel on
a dual Athlon 1800+ (1.5 GHz) machine with 256 MB of RAM and a 20 GB
IDE HDD. I have devfsd package installed:
$ dpkg -l devfsd
ii devfsd 1.3.24-1 Daemon for the device filesystem
I have enabled the mounting of devfsd during boot (not using the boot
option, but in the startup scripts):
$ grep devfs /proc/mounts
none /dev devfs rw 0 0
The current limitation on the number of NFS mounts has to do with the
major/minor number scheme currently in use by the kernel. Since the
minor numbers are only 8-bit and only a single major number is assigned
to NFS (UNNAMED_MAJOR), you can only mount about 256 NFS partitions.
Since one of the goals of devfs is to get away from the 8-bit
major/minor limitation, I had hoped I could just use it and it would
allow me to mount as many NFS partitions as I want. This didn't work,
but I am not exactly sure where the problem lies. Here a couple
guesses:
- Since devfs still must export major and minor numbers to the
userspace it does not by default totally ignore kernel major/minor
limitations
- perhaps I need a patched mount program that understands devfs
Whether it is one of these (or both) or something else, I am at a loss
as to how to go forward.
Other Attempts to Fix
---------------------
- Using automount doesn't work on my system because in our current
environment many of the NFS mount points are at /. Therefore they
each require a separate automount process. Each automount process
also seems to take up a minor from UNNAMED_MAJOR (and when its
mounted it will take up another, making the situation even worse).
- Currently there is an experimental patch to the kernel (and mount
and nfsd) which allows the mounting of more NFS partitions by
increasing the number of major numbers assigned to UNNAMED_MAJOR
from 1 to 4 (256 mounts -> 1024 mounts). While this may work, it
seems to me that devfs would be a more elegant and long term
solution.
Any help would be greatly appreciated. We are trying to move from Sun
to Linux and this is a major (pun intended?) sticking point since the
Sun machine happily mount our 300 NFS filesystems.
dd
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David Dooling
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