network raid possible?

[Igor Gueths]

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Its true tht Nfs provides shared storage. However, the reason I can't 
use Nfs is because if say my server goes down, there goes the shared 
filesystem. That is, assuming that Nfs has no mechanism of mirroring 
parts/entire filesystems on different machines. In other words, one 
modification on one server instantly beghins to proppogate to the rest 
of the machines. The best sollution I have found thus far is 
http://nbd.sourceforge.net for what I am looking for. However, it seems 
its not ready for production use.
On Wed, Mar 24, 2004 at 10:18:59PM +0000, Garry Turkington wrote:
> Hi,
> 
> If you're basically building a high-volume web farm then don't reinvent
> the wheel and use standard deployment architectures.  Having the content
> on a NFS server behind the web servers is an attractive and potentially
> low cost route, even gigabit networking is relatively affordable these
> days.  If fully shared storage is *truly* what you need then NFS is the
> easiest option.
> 
> Also, think about the likely data access patterns.  Do you have large
> amounts of static content?  If so then this could be local on each server,
> leaving only the truly dynamic content requiring the shared storage.  That
> likely allows you to get away with a less beefy NFS server and back-end
> network.
> 
> I'd also ask you to take a very long hard look at the stated requirement
> for instantaneous synchronisation across the multiple servers.  Building a
> highly available web service is exceptionally difficult if the requirement
> list includes phrases such as instantaneous, "fully transparent" and "no
> single points of failure".  What you really need to understand is the
> implication of the possible failure scenarios and just what impact that
> will have on the service clients.  Often when cost and complexity are
> taken into account the requirements soften somewhat.  Otherwise you end up
> designing systems where you want to have users in pairs in case one
> spontaneously combusts.  You can push points of failure further up and
> downstream but at some point you have to accept some risk.
> 
> Regards,
> Garry
> 
> Garry Turkington
> garry.turkington at acm.org
> 
> 
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