Re: Poor raid 1 performance?

In news:43938fba$0$44448$892e7fe2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx,
Folkert Rienstra va escriure:
> "Antoine Leca" <root@xxxxxxxxxxxxxxxxx> wrote in message
> news:439089e4$0$21227$626a54ce@xxxxxxxxxxxx
>> With RAID 1, you cannot make them contiguous or near enough for
>> both writing [every sector] and reading [every two sectors].
>
> So that's obviously not the way to do it.

Sorry, you are too terse for me. Which "way" are you writing about?


>> So the obvious organisation is to make OK for writing (so just like
>> a normal disk), and while sequential reading you should wait while
>> skipping the odd-numbered sector which is in between.
>
> That's silly.

May I ask you how it should be done then?


> You divide a single request into two and send each half to a
> different drive. With consequtive requests (for a sequential file)
> you sent half the number of total requests to one drive and the
> other half to the other one, resulting in both drives reading
> sequentially.

Sure, sorry I had assumed this explanation.
And since the media have been written sequentially (I assume it, but I'd
happy to learn a better way), if you are reading all the even-numbered
(resp. odd-numbered) sectors, so the disk controler have to wait for the
media a small bit between each sector to be transferred, which should give a
small penalty with respect to a non-RAID configuration (assuming media
access is the bottleneck, that is).


>> There is a gain though (half traffic on the wire, for example),
>
> That's not a perceptive gain.

/Quite/ possible ;-).


Antoine

.

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