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Date:      Wed, 6 May 2020 15:19:16 -0500
From:      Valeri Galtsev <galtsev@kicp.uchicago.edu>
To:        freebsd-questions@freebsd.org
Subject:   Re: redesignde the unix-like system directory
Message-ID:  <3f899735-1ed2-105c-1483-0450b8dcc7a3@kicp.uchicago.edu>
In-Reply-To: <20200506134457056426360@bob.proulx.com>
References:  <83788746a7d8a802d8af4b582e00827166febd1a.camel@tom.com> <CAEJNuHzCcqR0-v_SEPT4QWai1owzL_41M-YN3fTS_YGHN0jwFg@mail.gmail.com> <9a387b42-8da5-2968-24ba-754c3e461252@kicp.uchicago.edu> <20200506151230.GI82984@trajan.stk.cx> <c3f5a607-760d-8a85-c0f3-e72ee6b9a3dc@tundraware.com> <20200506134457056426360@bob.proulx.com>

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On 5/6/20 2:55 PM, Bob Proulx wrote:
> Tim Daneliuk wrote:
>> Arne Steinkamm wrote:
>>>>> /cloud, various cloud applications
>>>>> /net,  network information and server information, etc.
>>> Looking at a flat layout like this one gives me a feeling, that
>>> most people forgot that it's a real bad idea to have a
>>> external mounted directory in the root directory... easy way to make
>>> a system unresponsive in case of a network problem.
>>
>> Can you say a bit more about why this is so?
> 
> Assume NFS for simplicity.  A mount point at the /nfsmount1 directory.
> Then run "ls -l /".  That needs to stat(2) each entry in / and hits
> /nfsmount1

Do people really do that? I kind of since forever use automounter or 
similar, net mounts are in subdirectories of

/net

and - this is what _I_ do, not elegant thing, but convenient for my 
users - I make directories in / named after names of cross mounted 
machines, and put there symlinks to where automounter will mount 
exported from these machines directories, like

/machine1name/data1 --> ../mnt/machine1name/data1

Never had trouble you describe, and nicety of automounter is "nothing 
gets hang": once NFS server doesn't respond, mounts are unmounted 
seamlessly by automounter. And are mounted again when someone tries to 
access them and server is accessible.

Valeri

> with stat(2) which if the nfs server is not responding
> cannot return an answer to the query.  A lot of daemons and cron jobs
> will assume that the file system root and all entries in there are
> available and will trigger this problem as a byproduct of their
> operations.  I am just describing "ls -l" as the simplest way to
> trigger the issue.  "NFS server not responding."  This can be a reason
> for a system load of hundreds or thousands as process slots fill up
> with stuck processes blocked waiting for I/O from an unresponsive server.
> 
> However in the proposal I think the entries I quoted were for use as a
> subdirectory and not to have a mount point directly in root.
> 
>>> I keep the traditional filesystem layout
> 
> +1.  I prefer the traditional file system organization.
> 
> Bob
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-- 
++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++



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