On Tue, May 31, 2011 at 06:57:53PM -0400, Edward Ned Harvey wrote: > If you make it a 3-way mirror, your write performance will be unaffected, > but your read performance will increase 50% over a 2-way mirror. All 3 > drives can read different data simultaneously for the net effect of 3x a > single disk read performance.
This would be my recommendation too, but for the sake of completeness, there are other options that may provide better performance improvement (at a cost) depending on your needs. Namely, leave the third drive on the shelf as a cold spare, and use the third sata connector for an ssd, as L2ARC, ZIL or even possibly both (which will affect selection of which device to use). L2ARC is likely to improve read latency (on average) even more than a third submirror. ZIL will be unmirrored, but may improve writes at an acceptable risk for development system. If this risk is acceptable, you may wish to consider whether setting sync=disabled is also acceptable at least for certain datasets. Finally, if you're considering spending money, can you increase the RAM instead? If so, do that first. -- Dan.
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