Does ZFS in mirror mode double vdev read performance?

I'm not able to find a clear yes/no answer to this simple question: does using ZFS in mirror mode double the read performance of the underlying vdevs?

This applies to either individual requests or net performance (i.e. a single read request is sharded across two disks or two simultaneous requests are each served simultaneously from different disks).

If using Linux/FreeBSD (also FreeNAS) read speed is much better

Source: http://open-zfs.org/wiki/Features#Improve_N-way_mirror_read_performance It's hard to tell whether illumos/OSX have that patch which rebalances read I/O to the least busy device, or just improved round-robin.

In any case, mirror improves read I/O. As the other answer mentions, using SSDs usually doubles read I/O, while spinning drives increase performance by less than double depending on type of load.

My anecdotal testing on Linux shows a significant speed increase, especially when reading large files or more at the same time.

(Edited to reflect changes since the answer was posted)

This depends on the ZFS implementation and the Hardware you are using.

These benchmarks https://calomel.org/zfs_raid_speed_capacity.html provide a quick overview of the mirrored/striped performance, measured on FreeBSD.

As you can see, the read performance is doubled with SSDs and increased by approximately 50% with HDDs.