[OpenIndiana-discuss] Recommendations for fast storage

[alka]

ZFS datablocks are also a power of two what means, that if you have 
1,2,4,8,16,32,.. datadisks, every write is evenly spread over all disks.

If you add one disk ex from 8 to 9 datadisks, any one disk is not used on a read/write.
Does that means, 9 datadisks are slower than 8 disks?

No,  9 disks are faster, maybee not 1/9 faster but faster.
So think about more like a myth 

Add Raid redundancy disks to that count, example with 8 datadisks,  
add one disk for Z1 (9), 2 disks for Z2 (10) and 3 disks forZ3(11) for disks per vdev.




Am 16.04.2013 um 23:37 schrieb Timothy Coalson:

> On Tue, Apr 16, 2013 at 4:29 PM, Sašo Kiselkov <skiselkov.ml at gmail.com>wrote:
> 
>> If you are IOPS constrained, then yes, raid-zn will be slower, simply
>> because any read needs to hit all data drives in the stripe. This is
>> even worse on writes if the raidz has bad geometry (number of data
>> drives isn't a power of 2).
>> 
> 
> Off topic slightly, but I have always wondered at this - what exactly
> causes non-power of 2 plus number of parities geometries to be slower, and
> by how much?  I tested for this effect with some consumer drives, comparing
> 8+2 and 10+2, and didn't see much of a penalty (though the only random test
> I did was read, our workload is highly sequential so it wasn't important).
> 
> Tim
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