Discussion
Not had much cause to look into such things in the past and as you are an immensely knowledgeable bunch.
How easy is it to get two pcs of identical configuration doing identical things in pretty much real time?
I know it can be done, just cant find anything specific at the mo.
Any experiences chaps?
How easy is it to get two pcs of identical configuration doing identical things in pretty much real time?
I know it can be done, just cant find anything specific at the mo.
Any experiences chaps?
Can be done via some fancy software, but pricey.
Can't remember who - it was a few years ago that I looked but search for "Server Mirroring Software" on google and it'll get you some answers.
Done most effectively via IP over a network, it gives near as dammit redundancy, and if used over a WAN, locational redundancy - a useful thing in this day and age.
However, the cooler and more useful/valuble the service the higher the cost...
Can't remember who - it was a few years ago that I looked but search for "Server Mirroring Software" on google and it'll get you some answers.
Done most effectively via IP over a network, it gives near as dammit redundancy, and if used over a WAN, locational redundancy - a useful thing in this day and age.
However, the cooler and more useful/valuble the service the higher the cost...
Edited by neil_cardiff on Monday 12th June 16:33
I was offered it on a server we're currently using as our production SQL Server box. It sounds great, but when I thought about it a bit it struck me as potentially a bit of an arse. I was told that the replication effectively worked at the level of the disc controller ... i.e. you write a byte to the disc, and it gets mirrored to the remote machine. Well that's all fine and dandy, but what happens if that write instruction is the one that corrupts my crappy Windows 2000 Server box or corrupts my poxy SQL Server database? Do I want that byte meticulously mirrored onto by back-up server rendering both boxes screwed? If my main box collapses in a heap as its discs eat themselves or the PSUs melt, do I have any guarantee that write operations will complete cleanly? If my network cards go pop, what state will the remote discs be in?
As is often the case, the IT boys had no answers and looked dissapointed. It may well be that there is some magic solution to these problems ... if there isn't, I can't imagine why anyone would use this stuff. But the IT boys didn't have the answers so I had to reject that solution in favour of something we actually understood. Instead I pick a few times in the day when our main server is in a "well defined state" (it is not a continuous transaction processing system), back it up, move the files to the remote box and restore them ... dumb, put reliable.
We've thus forgone the possibility of having near instantaneous fail-over in order to have a higher chance of being able to switch to a back-up server that is still runnig and whose business data is in a well-understood state.
I'd be very interested to hear if and how other people are using this kind of mirroring, coz if it can get around the kind of problems I outlined above, it would be great.
As is often the case, the IT boys had no answers and looked dissapointed. It may well be that there is some magic solution to these problems ... if there isn't, I can't imagine why anyone would use this stuff. But the IT boys didn't have the answers so I had to reject that solution in favour of something we actually understood. Instead I pick a few times in the day when our main server is in a "well defined state" (it is not a continuous transaction processing system), back it up, move the files to the remote box and restore them ... dumb, put reliable.
We've thus forgone the possibility of having near instantaneous fail-over in order to have a higher chance of being able to switch to a back-up server that is still runnig and whose business data is in a well-understood state.
I'd be very interested to hear if and how other people are using this kind of mirroring, coz if it can get around the kind of problems I outlined above, it would be great.
It's a nasty area. Really depends on what you want to mirror (and you need to list EVERY service, process, file here). If you're looking for a plug and play solution where you just get your app and it'll work you really need to be talking redundent hardware rather than 2 PCs.
Played with the Tanden Non-Stop stuff for a bit. Very nice. Very expensive. In the end just built our own software solution.
Played with the Tanden Non-Stop stuff for a bit. Very nice. Very expensive. In the end just built our own software solution.
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