[OpenIndiana-discuss] Recommendations for fast storage

[Jay Heyl]

On Tue, Apr 16, 2013 at 5:49 PM, Jim Klimov <jimklimov at cos.ru> wrote:

> On 2013-04-17 02:10, Jay Heyl wrote:
>
>> Not to get into bickering about semantics, but I asked, "Or am I wrong
>> about reads being issued in parallel to all the mirrors in the array?", to
>> which you replied, "Yes, in normal case... this assumption is wrong... but
>> reads should be in parallel." (Ellipses intended for clarity, not argument
>> munging.) If reads are in parallel, then it seems as though my assumption
>> is correct. I realize the system will discard data from all but the first
>> reads and that using only the first response can improve performance, but
>> in terms of number of IOPs, which is where I intended to go with this, it
>> seems to me the mirrored system will have at least as many if not more
>> than
>> the raid-zn system.
>>
>> Or have I completely misunderstood what you intended to say?
>>
>
> Um, right... I got torn between several letters and forgot the details
> of one. So, here's what I replied to with poor wording - *I thought you
> meant* "A single read request from a program would be redirected as a
> series of parallel requests to mirror components asking for the same
> data, whichever one answers first" - this is no, the "wrong" in my
> reply. Unless the first device to answer returns garbage (something
> that doesn't match the expected checksum), other copies are not read
> as part of this request.
>

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.