Re: raid1 does not seem faster

[Bill Davidsen <davidsen@tmr.com>]

Iustin Pop wrote:
> On Wed, Apr 04, 2007 at 07:11:50PM -0400, Bill Davidsen wrote:
>   
>> You are correct, but I think if an optimization were to be done, some 
>> balance between the read time, seek time, and read size could be done. 
>> Using more than one drive only makes sense when the read transfer time is 
>> significantly longer than the seek time. With an aggressive readahead set 
>> for the array that would happen regularly.
>>
>> It's possible, it just takes the time to do it, like many other "nice" 
>> things.
>>     
>
> Maybe yes, but why optimise the single-reader case? raid1 already can
> read in parallel from the drives when multiple processes read from the
> raid1. Optimising the single reader can help in hdparm or other
> benchmark cases, but in real life I see very often the total throughput
> of a (two drive) raid1 being around two times the throughput of a single
> drive.

Why optimize the single thread case? Any process which has low CPU 
requirements (by current standards) becomes i/o bound. The obvious 
candidates are grep, sed, dd, or awk. And don't overlook the benefits of 
reliable swap.

Test script modifications taking place as I type, I post the script and 
some results later this week, barring urgent support issues.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979