Referencing your response to a question posed on Oct. 16, 2002 regarding mirroring to different subsystems, I understand your position of a "sticky sweet beverage bath" on a single subsystem. However, I'd like you to explain your comment about "All storage subsystems have single points of failure, including Clariion boxes." Please tell me the single point of failure on a Clariion array (outside of a bath) as you intimate "Consider the power source, the cache boards, internal controllers" might be SPOF in the Clariion platform.
Also, how do you recommend "mirroring" to another subsystem via software copy or true hardware split-mirror?
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The container itself is a single point of failure on ALL single-box hardware systems whether Clariion or another brand of system, whether disk array or computer system. I only called out Clariion in the answer because it was mentioned in the question. I am not aware of anything special about the container for a Clariion that makes it more or less susceptible to damage.
I am not intimately familiar with the architecture of a Clariion but all of the disk arrays that I have seen use a single backplane (or equivalent) that can be a single point of failure (though admittedly a rare point of failure). Most arrays have engineered the power supply, fuses, power cords, etc., out as single points of failure, but others remain.
If money were no object, I would always recommend mirrored from one disk array to another. Since money is an object, though, it is necessary to balance the cost of the extra arrays with the potential for downtime if an unfortunate incident were to occur.
I would perform array-to-array mirroring via software, since I am not aware of any hardware-based solution that would permit mirroring between two arrays. Hardware split-mirrors are not the answer since again, all disks must be in the same array.
Hope this is helpful.
Evan L. Marcus
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This was first published in December 2002