Re: placiing content and application on a microsoft DFS solution

2010-06-22 Thread Peter Crowther 
On 22 June 2010 16:10, M.H.G. Emmerig m.h.g.emme...@dnb.nl wrote:



 Has anyone ever placed an application and its content on a redundant DFS
 solution?
 So as when one DFS server fails, another takes over.
 Does anyone see possible problems with this setup?
 ie. when dfs server fails does tomcat loose connection to the app or is the
 failover fast enough.

 At best, the failover takes several seconds, during which your app will
fail to respond.  Depending on your load and application design, the queued
requests may be sufficient to run you out of heap memory, database handles
and similar.

I assume your goal is to improve reliability of end-user access to your
application.  If you have to use Windows, why would you take a DFS approach
rather than using Windows' file replication to replicate files to multiple
servers?  The probability of network failure or poor performance is orders
of magnitude higher than the probability of HDD subsystem failure or poor
performance, so I would expect accessing apps from a remote network drive to
worsen your reliability rather than improve it.

- Peter

RE: placiing content and application on a microsoft DFS solution

2010-06-22 Thread Robinson, Eric 
 
 Has anyone ever placed an application and its content on a redundant 
 DFS solution?
 So as when one DFS server fails, another takes over.
 Does anyone see possible problems with this setup?
 ie. when dfs server fails does tomcat loose connection to the app or 
 is the failover fast enough.

DFS is based on the Windows Change Journal. There can be several seconds
to a minute of latency before file changes replicate from one DFS server
to the other. Be sure that your application could tolerate that. If I
was going to try a DFS-based approach, I'd just run DFS right on the
tomcat server(s). However, my experience with DFS has been
unsatifactory. Replication often drives up average disk queue lengths on
both servers and causes application-level freezes.

Personally, I'd strongly recommend using Linux+DRBD+Pacemaker. Much
faster and more stable.

--
Eric Robinson


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