On May 5, 2012, at 8:04 AM, Bob Friesenhahn wrote:

> On Fri, 4 May 2012, Erik Trimble wrote:
>> predictable, and the backing store is still only giving 1 disk's IOPS.   The 
>> RAIDZ* may, however, give you significantly more throughput (in MB/s) than a 
>> single disk if you do a lot of sequential read or write.
> Has someone done real-world measurements which indicate that raidz* actually 
> provides better sequential read or write than simple mirroring with the same 
> number of disks?  While it seems that there should be an advantage, I don't 
> recall seeing posted evidence of such. If there was a measurable advantage, 
> it would be under conditions which are unlikely in the real world.

Why would one expect raidz to be faster? Mirrors will always win on reads 
because you
read from all sides of the mirror. 

Writes are a bit more difficult to predict and measure, mostly because ZFS 
writes to the 
pool are async.

> The only thing totally clear to me is that raidz* provides better storage 
> efficiency than mirroring and that raidz1 is dangerous with large disks.

space, performance, dependability: pick two
 -- richard

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