Sunday, 19 January 2014

Storage Spaces again

Came across this, admittedly old, discussion about Storage Spaces http://www.eightforums.com/general-support/15887-storage-spaces-questions.html

The fun starts at around post #4, with a real good piece of advice - your setting up a large drive system, read a LOT before committing your data to it for good.

Then the discussion touches the Drive Extender briefly. Storage Spaces is not Drive Extender. Indeed it is not. Storage Spaces is arguably more fragile, and undoubtedly Storage Spaces is more difficult to recover once failed. Way more difficult, I'd venture to say.

Then, around post #8, virtual machines come up. The common misconception is that recovery from storage system failures can be practiced with virtual machines. You'd better not. Virtual machines are good for modeling and training some normal operations of a storage system, but they are abysmal in reproducing storage behavior in failures.

In a virtual machine, all hardware is fail-stop. You cannot simulate bad blocks with any fidelity using a virtual machine. The same goes for any kind of hardware problem. Virtual machine cannot have transient errors of its own. The only situation you can model with a reasonable accuracy is a complete failure of a hard drive (or several of them) on reboot. In real life, you get all kinds of unadulterated hardware problems: timeouts, bad sectors, power transients, defective cables, stuck fans and overheat. At the end of the day, what matters is the response of the storage system to an endless list of real-world, real-hardware problems, and none of these you can reproduce with a virtual machine.

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