While I appreciate the limitations of funds and of technology choices, these - 
by definition - limit your synchronization choices and will probably impose a 
set of reasonably hard and quantifiable limits on how close you can get to 
"realtime".  This can be modeled but only with intimate knowledge of the 
application, the environment, and its inner workings.

There have been some good suggestions for investigation that have been 
mentioned in prior posts.

"almost always changing" and "a few seconds out" and "critical" are 
unfortunately not quantified terms.  Having a handful of dynamic files get 
written to your primary disk every minute with the ability to take a minute to 
sychnronize them to the secondary with only the implication that people may 
have to wait 60 seconds to get their files is decidedly different than having 
thousands of files moving around (immediate disk I/O implication, nevermind 
application locking and scaling issues for both the main app and the 
synchronization process) with legal implications.

Get this sorted out and back it with data points and you'll likely solve your 
own problem - which is whether you need a Symmetrix with SRDF down through to 
a set of rsync processes to a rewrite of your app to write the files 
consecutively to primary then the secondary. 


quoted text
>I dont have unlimited funds, this is tech that I can afford to get the job
>done between two points that 1,928 feet apart. What im using to transmit the
>data though is not the problem, the problem is how to accomplish my goals on
>the software side.  Any suggestions on that part Jason?
>
>On Tue, Aug 26, 2008 at 7:42 PM, Jason George <lists@masterplan.org> wrote:
>
>> >I have a file based database with a mail server and public document
>> >storage.  I need to replicate all that data to a server that is
>> >exactly the same but off site from the main one.  Storage of the
>> >database is almost always changing and can only be a few seconds out
>> >of sync from the offsite server due to the critical nature of the
>> >data.  They will be sending across a 802.11n point to point wireless
>> >dedicated to the process.
>> >
>>
>> So you have critical, time-sensitive data, yet you are using unlicensed
>> wireless spectrum and draft radio technology?
>>
>> Just trying to understand the real parameters of your setup versus those
>> which
>> are just perceived...
>>
>>
>> --Licensed-microwave-carrying-realtime-utility-traffic guy