Why all raid devices do have zero 'time in queue' value?

Why all raid devices do have zero 'time in queue' value?

[George Shuklin]

Good day.

I've look to stat for all MD devices I have (raid0, raid1, raid10) - all 
of them reports 0 for time_in_queue field in /sys/block/mdX/stat file.

Is any reason why all raid devices contains no information about time 
spent on requests processing?

Thanks.

Re: Why all raid devices do have zero 'time in queue' value?

[NeilBrown]

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On Sun, 11 Mar 2012 02:33:34 +0400 George Shuklin <george.shuklin@gmail.com>
wrote:

> Good day.
> 
> I've look to stat for all MD devices I have (raid0, raid1, raid10) - all 
> of them reports 0 for time_in_queue field in /sys/block/mdX/stat file.
> 
> Is any reason why all raid devices contains no information about time 
> spent on requests processing?
> 

Wrong mailing list for MD - you want linux-raid@vger.kernel.org

But I can still answer :

These raid levels don't queue requests at all.  They just pass them straight
to the relevant underlying devices.

(Now admittedly RAID5 does queue requests but doesn't set the time_in_queue
field, but that is a separate issue).

If you really care about time_in_queue, you need to look at the queues of the
member devices.

NeilBrown

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