ftpfs (was: Re: HD cloning)

Timm Murray admin at madtimes.com
Fri Dec 15 17:00:43 EST 2000


A while back, I got an idea for an 'ftpfs', literaly mounting an FTP
store as a regular file system.  I wasn't sure if this had ever been 
tried before, and I'm still not sure how many other OSes have it.
However, I recently started playing with GNU HURD and learned 
that it does have an ftpfs!  The code for it is apparently old
(1997 was the last change log entry) and the maintainer has since
left the FSF.

Would an ftpfs work better then NFS (security, speed, reliability, 
etc.)?  Are there currenly any patches for such a thing for Linux?  

Please note that I have just started using the HURD, so I don't
know too much about it.

Donald Becker wrote on 12/5/00 12:34 pm:

>On Wed, 6 Dec 2000, Bruce 
>Janson wrote:
>> From: Daniel Ridge 
><newt at scyld.com>
>>     On Wed, 6 Dec 2000, 
>Bruce Janson wrote:
>>     > Like you, installing 
>makes me grumpy too, so I 
>try not to do it
>>     > more than once.  
>Ideally all of our compute 
>servers would share
>>     > the same (network) 
>file system.  There are ways 
>of doing this
>>     > now (typically via NFS) 
>but they tend to be 
>hand-crafted and
>>     > unpopular.
>>     > In particular, I notice 
>that the recent Scyld 
>distribution
>>     > assumes that files 
>(libraries if I remember 
>rightly) will be
>>     > installed and available 
>on the local computer.
>>     > Why do people want to 
>install locally?  (Scyld people 
>in particular
>>     > are encouraged to 
>reply.)
>>     
>>     While it is true that our 
>(Scyld's) distribution places 
>some files  on target nodes, 
>the total volume is pretty 
>tiny (a couple of tens of  
>megabytes for now, less in 
>the future). These files, 
>essentially  all shared 
>libraries, are placed on the 
>nodes just as a cache and  
>are not 'available' from most 
>useful perspectives. They 
>are 'available'  for a remote 
>application to 'dlopen()' or 
>certain other dynamic link  
>operations.
>> Yes, but storing any files 
>locally suggests that you 
>don't trust the  kernel's 
>network file system caching.  
>Is that why?  If so, in what  
>way does such caching fail?
>...
>> Sounds like you don't use a 
>network file system at all,  
>which in itself is an 
>interesting decision.  Care to 
>give some reasons?
>
>A common misperception 
>when people first see the 
>Scyld Beowulf system is that 
>it is based on a NFS root 
>scheme.
>Using a NFS root has several 
>problems:
>   NFS is very slow
>   NFS is unreliable
>   NFS file caching has 
>consistency and semantic 
>problems.
>
>Instead our model is based 
>on a ramdisk root and cache, 
>along with using 'bproc' to 
>migrate processes from a 
>master node.
>
>All of the NFS problems are 
>magnified and multiplied 
>when working on a Beowulf 
>cluster.  Unlike a workstation 
>network, where users are 
>idle on average and working 
>on different jobs, a cluster is 
>all about hot spots. The NFS 
>server quickly becomes a 
>major serialization point.  
>(The same observation is 
>true of a NIS/Yellow-Pages 
>server: when starting a 
>cluster job, every processor 
>will try to scan the password 
>list at the same time.)
>
>While a ramdisk root initially 
>sounds like a waste of 
>memory, the semantics of a 
>ramdisk fits very well with 
>what we are doing.  The 
>Linux ramdisk code is unified 
>with the buffer cache, 
>rather than a separate page 
>cache.  The files cached in 
>the root ramdisk are mostly 
>contain hot pages on a 
>running system: the "/", 
>/etc, /lib and /dev 
>directories, and the common 
>libraries.
>
>The unified cache means 
>that rather than costing 
>performance by wasting 
>40MB of ramdisk memory, 
>we have only have a few MB 
>of dead pages.  In some cases 
>we have a performance 
>improvement over a local 
>disk root by effectively 
>wiring down start-up library 
>pages that tend to 
>FIFO-thrash.
>
>>     In addition to shared 
>libraries, we also place a 
>number of entries  for '/dev' 
>on the nodes.
>> Well, now that you 
>mention /dev, why don't 
>you use devfs to 
>automatically  populate 
>your nodes' /dev 
>directories?
>
>The devfs addition is 
>controversial, at best.  It 
>would make our system 
>smaller and less complex, 
>and the drawback of 
>retaining non-standard 
>device ownership and 
>permissions is much reduced 
>on a slave node.  But we don't 
>want to introduce what some 
>perceive as a gratuitous 
>change on top of our 
>required changes.
>
>
>Donald Becker				
>becker at scyld.com
>Scyld Computing 
>Corporation		
>http://www.scyld.com
>410 Severn Ave. Suite 210	
>	Second Generation 
>Beowulf Clusters Annapolis 
>MD 21403			
>410-990-9993
>
>
>_____________________________
>__________________ Beowulf 
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>Beowulf at beowulf.org
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