Re: Does there exist something like a networked filestorage
From: Juhan Leemet (juhan_at_logicognosis.com)
Date: 07/20/04
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Date: Mon, 19 Jul 2004 21:05:02 -0200
On Mon, 19 Jul 2004 22:22:21 +0200, Someone wrote:
> I am not looking for things like Kazaa, eMule, and other p2p sharing
> filesystems.
>
> The problem I like to solve is the following :
>
> I want a very large amount of diskspace, lets say larger then one single PC can
> hold. I also have a number of "old" PCs and other boxes hanging around. I would
> now like to fill them up with hard disks (in general, they already are) connect
> them to a network but present them as one single filespace.
>
> My first naive idea was the following:
>
> on PC1, create a "shared folder" in /shared
> on PC2, create a "shared folder" in /shared
>
> Now on PC3 mount both, eg.
>
> mount -t nfs PC1:/shared /nwview
> mount -t nfs PC2:/shared /nwview
>
> However this 2nd command fails of course while /nwview has already been
> occupied. The problem is also not browsing the shared filespace but saving data
> into it. Eg. for browsing I could create scripts like dls which just, scans and
> sorts all the files on all the /shared folders of all PCs available. (In fact
> the p2p sharing filesystems could handle this...). The tricky part is of course
> transparantly write to this filespace as if it is just one single directory
> entry.
Use the automounter and indirect maps. That's how the /home directories
are assembled. They can be on different servers, for different users. That
does mean though that you will have to specify at least some
distinguishable directories in your indirect maps. I don't know of a way
to bundle a number of machines into a virtual disk concatenation over a
number of machines. The problem there would seem to be "who owns the
directories? inode allocations?" The NFS approach leaves each machine to
organize and manage its own file system space. The client machine(s) then
can assemble directories (view) that spans over several machines.
This is exactly how large installations of Sun Solaris (and other *nix)
are set up. They might use NIS, NIS+, LDAP or something else for name
lookups or authentication. The main part is NFS+automounter.
Personally, I use NIS (on a secure private network) and distribute the
automounter maps from my NIS master. There are some security issues with
NIS, but there are ways to solve them (e.g. secure RPC). YMMV
BTW, you can have a "default" server for all user homes, and then specify
selected users or groups (e.g all accounts starting with p* or in a
range, etc.) to reside on specific other NFS servers.
> I also would like to use this idea so that, when I need more diskspace,
> I can just add another network box. The approach should be such that
> none of the users need to change something.
Yes, that's easy. Setup the new machine and integrate it with your network
(esp. name lookup, and automounter maps, etc.). You do need a universal
lookup scheme. NFS only works if the uid and gid numbers are the same
between client and servers. Trying to maintain that by hand in server /etc
config files would be a nightmare (I've seen that go wrong). Set up right.
You can "move" (obviously only when they are inactive) users /home
directories from server to server and update the automounter maps and they
need not know that anything has changed, next time they log on. To be
safe, you should probably lock out the user login when you're relocating
his home directories, otherwise he will surely lose something (e.g.
written to old machine when transfer almost completed).
> Is it also possible to do this in a heterogenous NW, eg. boxes with both
> Linux/Windows (and in fact Solaris as well)
> I guess that, once i could set it up on a linux box, I could reexport this
> filespace again using Samba and make it available for the Win PC's as well.
I suppose. I don't think NFS likes reexporting imported NFS mount points.
The understanding is that you should mount from the "owning" computer, so
that you don't add vulnerability/reliability issues with intermediate gear.
Since Samba is just a "normal application" on *nix machines, it is more
tolerant, and in fact probably cannot distinguish between local/remote
files. I believe you can reexport with Samba.
-- Juhan Leemet Logicognosis, Inc.
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