Re: Awful RAID5 random read performance

[John Robinson <john.robinson@anonymous.org.uk>]

On 31/05/2009 18:19, Goswin von Brederlow wrote:
> John Robinson <john.robinson@anonymous.org.uk> writes:
>> Clearly when you're doing this over 4 drives you can have ~400
>> seeks/second but that's still limiting you to ~400 reads/second for
>> smallish block sizes.
> 
> Note that that only holds true for writes or multithreaded reads.
> Reading from a single thread will randomly pick one drive (depending
> on where it wants to read), wait for it to seek, read one block of
> data and repeat. So you get the speed of a single drive no matter how
> many drives there are in the raid.

Sure, that's why I said "can", but I thought iozone was multi-threaded. 
Maybe it needs an option specified, in which case using more threads 
than there are discs would be a good idea.

Cheers,

John.