On 16/07/10 12:31 PM, Daniel Pittman wrote:
Also, lots of different apps, so I might well end up with multiple
solutions. A good distributed POSIX FS with replication, eventual
consistency, some sensible conflict resolution model, and data center
awareness would have been easy enough to use though.
If I could have my pony. ;)
So as you and Jamie have both alluded to, this is a pretty hard problem
to solve. Most of the Enterprise-y solutions I deal with solve it by
pushing the problem down the stack and using $expensive_storage_array
with synchronous replication. Possibly over also $expensive_dwdm_fibre.
The most accessible of these solutions is probably NetApp's MetroCluster
tech. If you truly need real-time POSIX compliant synchronous access
between sites, this (and it's kin from HDS and EMC) is pretty much your
only choice.
Most of the other Open-Source (and indeed, commercial) solutions to
doing this at a filesystem-level have left me wanting. We tested and
deployed GlusterFS for a large customer project last year, purely for HA
file serving, and regretted it so much that we ripped it out in the
middle of a busy production period and replaced it with NFS + Rsync
(particularly after the customer revised their recovery time objective
:)). We've had similar amounts of pain with Microsoft's DFS solution (in
Windows land, ugh).
As Jamie notes, it's at this point that you'd usually go back and
redefine the problem, particularly after the sales dudes make your eyes
bleed. :)
There are a couple of different shapes this problem usually takes in the
market - "I want a DR site" or "I need to share files with a remote
branch". Considering these, and their various solutions (Publish/two+
subscribers, move the desktops closer to the data, active/passive
access, ...) might give you some more ideas about outside-the-box ways
to solve the problem.
Your mileage will almost certainly vary.
Cheers,
Matt
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