[mythtv-users] Shared filesystem that looks different to different machines

Hika van den Hoven hikavdh at gmail.com
Wed Jun 4 23:36:02 UTC 2014


Hoi Raymond,

Thursday, June 5, 2014, 1:21:14 AM, you wrote:

> On 6/4/2014 1:40 PM, Joseph Fry wrote:
>>
>>             I don't believe that NFS would have any issue with nesting a
>>             mount inside another mount like this, after all the OS just
>>             treats it as another filesystem and every linux system I
>>             have ever seen does this (/dev, /proc, etc).
>>
>>
>>         NFS can have issues if you mount one NFS volume within another
>>         NFS volume.  If access to the lower volume is ever anything but
>>         100% stable, and the mount point for the upper volume is lost,
>>         bad things happen.  It's the same reason why you never use an
>>         NFS share for swap space.
>>
>>
>>     Mounting one NFS filesystem on another NFS filesystem has been
>>     commonly used from the beginning of NFS: diskless systems did this
>>     all the time.
>>
>>
>> I could see problems like Raymond describes if it were two different NFS
>> servers and you were nesting... but on the same server, I'd imagine that
>> if one went, the other would as well anyway.

> I've had issues even when using only one NFS server. The mountpoint 
> basically becomes a black hole. Any process that tries to touch that 
> branch of the filesystem is irrecoverably blocked (SIGKILL can't even 
> touch them), and the system can only be fixed by a reboot.

The advised solution for a dirty NFS mount is to remount, which is
impossible if there are nested mounts. Sometimes a refresh on the NFS
server will help, but I have rarely see that work. Mounting the bottom
share read-only on all clients makes it rare that the mount gets
dirty, but not impossible. With nested mounts on net-clients they are
normally either read-only or exclusive to the client (the home
directory)


Tot mails,
  Hika                            mailto:hikavdh at gmail.com

"Zonder hoop kun je niet leven
Zonder leven is er geen hoop
Het eeuwige dilemma
Zeker als je hoop moet vernietigen om te kunnen overleven!"

De lerende Mens



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