Re: Hardware vs. Software RAID

No, Oracle ASM is not "similar to software RAID".

One of the features offered by ASM is software RAID. But this does not make ASM equal to software RAID.

And no, I would think it is never recommended to use software RAID (with ASM or otherwise) if hardware RAID (RAID-1) is available. At least, never recommended by me. I am unaware of any cirsumstance in which software raid is preferrable to hardware raid, except perhaps the case of very inexpensive / unreliable disk arrays, where the power is not redundant, or the storage integrity offered by the hardware is otherwise unacceptable. (Even then, you might be better off to purchase a better disk array...) Of course, in this case, you might still be using the Software RAID to augment the hardware RAID, not to replace it.

Aside from the ability to bridge across storage devices (disk arrays) I am unaware of any case where software RAID is superior to hardware RAID. And I am aware of numerous cases where it is clearly inferior.

Software RAID is -- in general -- superior to no RAID, and preferable too, although not usually for performance. You will always suffer a performance loss with Software RAID, whereas you will usually experience performance gains with most hardware RAID. Well, RAID-1, anyway. :-)

So, to finish answering the question, "am I saying that you should not use ASM?", of course not! ASM is a perfectly good tool, with perfrectly good uses. And software-supported data redundancy is one of them. However, that particular feature should probably not be used in preference to (adequate) hardware-based RAID.

Please note, that while I have plentiful (and good) reasons to prefer hardware RAID to software, the foregoing is simply my opinion. I am sure that (somewhere) there are others with differing opinions.

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Cheers,
-- Mark Brinsmead

   Senior DBA,
   The Pythian Group
   http://www.pythian.com/blogs

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