[clug] Clustering file systems, without excluding windows

[Paul TBBle Hampson]

[Disclaimer: This is work-related. Feel free to ignore it if you
would expect that answering this should be paid-consultant work.]

Everyone,

I've got a few servers together running an ISP, and it's currently
operating with basically RAID-1 and rdiff-backup across samba, at
least for the actual files. (Database backups are handled differently)

I'd like to move to some sort of clustered/NAS filesystem, both to
centralise at least one copy of the data someone I can back it up
without pulling it across the LAN, and partly so I can cluster the
various servers out.

I've been staring hard at this, and I'm not sure I've wrapped my head
around it completely, ever since Michael Still mentioned
ATA-over-Ethernet talking about a NSLU2 at CLUG one night.

If I'm understanding correctly, I put disks in a server, mdadm them into
a raid away, partition it (prolly with mdp, but I guess LVM is possible
too) and export the partitions with either AoE or iSCSI.

I then put a clustered file system on top of that, which runs on each
machine accessing the exported block devices as local device names, but
distributing locking using something like DLM.

For the mail spool, that looks quite safe and easy. I then throw vserver
in front to handle POP3 (or simply an iptables rule + heartbeat would
sort that one out) and I can run SMTP servers on as many machines as I
like, at least for incoming email. And voila, distributed mail hosting.
(Well, I dunno how I'm going to handle mailman yet... Luckily, mailman
is always its own domain, so I can easily just have a dedicated mailman
machine again with heartbeatd or something.)

Since I'm using postfix, and only one machine can use a specific spool,
I can't do the same thing for outgoing email... I guess I could, and if
one of the outgoing machines catches file, the risk is only to stuff in
that one's spool. That'll save me having to try and split one DNS entry
"mail" into "smtp" and "mx", given the swathe of hosted clients.

The problem arises from web service. Specifically, the IIS machine. What
I'd like is to have it use the same file hierarchy as the linux web
servers, so I can unify the various site-creation scripts and pathname
expectations.

I haven't seen a free clustered file system that includes a Windows
client, so I'm thinking I throw samba on one of the machines in the
cluster, and export the tree to the windows machine.

Has anyone tried having a single samba exporting a cluster-shared file
system like this, and/or run into any problems trying?

This'd also allow me to distribute FTP access to website directories,
which'd be nice.

The other big advantage is I could test sites for migration off the IIS
server without having to actually copy the data onto one of the linux
webservers and try it, but just by adding the appropriate Apache config
snippet.

If anyone's got any comments or suggetions, I'd love to hear them. As I
say, I'm having a little trouble getting my head around this in the
limited time I have to throw at such things.

-- 
-----------------------------------------------------------
Paul "TBBle" Hampson, B.Sc, LPI, MCSE
Very-later-year Asian Studies student, ANU
The Boss, Bubblesworth Pty Ltd (ABN: 51 095 284 361)
Paul.Hampson at Pobox.com

Of course Pacman didn't influence us as kids. If it did,
we'd be running around in darkened rooms, popping pills and
listening to repetitive music.
 -- Kristian Wilson, Nintendo, Inc, 1989

License: http://creativecommons.org/licenses/by/2.1/au/
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