does the mirrorred swap have poorer performance than nonmirrored?

[faust2004]

thank
Sunny

[Thierry Poels_1]

Hi,

mirroring has always a very small impact on performance.
But consider the alternative: if a disk crashes, you will loose your swap, your system might crash or at least require a reboot to continue working normally.

regards,
Thierry.

[harry d brown jr]

Sunny,

You have to ask yourself, is performance worth more to my company than data protection. Basically should you be more concerned about how fast a transaction processes than how to ensure that you can safely protect your company from potential data loss.

live free or die
harry

[Patrick Wallek]

In todays computing environment one should not be too concerned with the performance of swap. Why? Because you should NEVER have to use swap. Memory is cheap enough, especially 3rd party non-HP memory (sorry HP). So you should buy enough RAM for your machine such that you never ever have to touch the swap area.

As said, mirroring will always have a small performance impact, but it is more that worth it for the redundancy. If you don't mirror swap, and you do have to swap out some processes, and the disks swap is on goes bad, then you have a very good chance of crashing your machine. And how much would recovering that machine cost in time, resources and actually $$$$?

[harry d brown jr]

Patrick, If you don't mirror swap, and don't allocate disk space for it, how would one boot from the mirrored copy?

live free or die
harry

[Patrick Wallek]

How would you boot from a mirrored OS disk with no pri. swap? Uhmmmm....... Very carefully?! I honestly don't know what would happen if you tried to boot without pri. swap. Never tried it and I'm not sure I want to.

[harry d brown jr]

Patrick,

I haven't hAd to do it in a very long time, but I remember that we had issues because we hadn't made a primary swap area mirrored. But I also think there is a way. I think I'll look it up monday.

have a great weekend!

live free or die
harry

[A. Clay Stephenson]

Hi:

It's rather difficult (and silly) to talk about performance and swap in the same topic. The impact will be same and trivial compared to the downtime caused by no mirror.

[harry d brown jr]

Patrick, I agree, I originally misread the question, I missed the "swap" part. Must of had one or two too many last night :-))


live free or die
harry

[Bill Hassell]

It's very important to think of swap as a MASSIVE degradation in performance, between 50:1 and 500:1 depending on how badly the system is paging. Many years ago, when 128 megs of RAM was huge, swapping was inevitable and all sorts of methods were developed (swap priority, raw versus filesystem) to allow lots of programs to run at the same time, albeit incredibly slow.

Today, swap space performance is unimportant since it should be used only occasionally by interactive programs and emory mapped files. Mirroring is important for swap space because it is part of virtual memory and if it fails, the system will likely panic, even if it is only a couple of pages of an unimportant program.