Re: Performance problem - reads slower than writes

Brian Candler
2012-01-31T21:52:14Z

On Tue, Jan 31, 2012 at 09:52:05AM -0500, Christoph Hellwig wrote:
> You don't just read a single file at a time but multiple ones, don't
> you?

It's sequential at the moment, although I'll do further tests with the -c
(concurrency) option to bonnie++

> Try playing with the following tweaks to get larger I/O to the disk:
>
> a) make sure you use the noop or deadline elevators
> b) increase /sys/block/sdX/queue/max_sectors_kb from its low default
> c) dramatically increase /sys/devices/virtual/bdi/<major>:<minor>/read_ahead_kb

Thank you very much: I will do further tests with these.

Is the read_ahead_kb knob aware of file boundaries? That is, is there any
risk that if I set it too large it would read useless blocks past the end of
the file?

Regards,

Brian.