[OpenIndiana-discuss] Recommendations for fast storage

[Edward Ned Harvey (openindiana)]

> From: Jay Heyl [mailto:jay at frelled.us]
> 
> Ah, that makes much more sense. Thanks for the clarification. Now that you
> put it that way I have to wonder how I ever came under the impression it
> was any other way.

I've gotten lost in the numerous mis-communications of this thread, but just to make sure there is no confusion:

If you have a mirror (or any vdev with redundancy, radizN) you issue a read, then normally only one side of the mirror gets read (not the redundant copies.)  If the cksum fails, then redundant copies are read successively, until a successful cksum is found (still, some redundant copies might not have been read.)

If you perform a scrub, then all copies of all information are read and validated.

The advantage of reading only one side of the mirror is performance.  If one device is busy satisfying one read request, then the other sides of the mirror are available to satisfy other read requests.