On Wed, Jun 01, 2011 at 10:16:28AM +1000, Daniel Carosone wrote: > 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.
In fact, I should state even more clearly: do this, since there is very little reason not to. Measure the benefit. Move on to the other things if the benefit is not enough. When doing so, consider what kind of benefit you're looking for. > 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. > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
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