[CentOS] slow i/o with a raid 50 on a 3ware controller

[Markus Falb]

On 7.8.2014 03:04, John R Pierce wrote:
> On 8/6/2014 5:32 PM, Markus Falb wrote:
>> Do you have barriers enabled?
>> Just another shot in the dark, but 5 didn't have that.
>> If you have battery backed Cache with your Controller, you can safely
>> disable barriers anyway.
> are you sure about this?  thats not my understanding.
> 
> What I've been told is, the battery backed write cache just lets you 
> enable writeback caching in the raid controller, write barriers at the 
> various OS layers still have to be respected, as they ensure certain 
> writes are completed in order.

You mean there are other places besides the drive itself where I/O may
be reordered? The I/O Scheduler maybe? Hmmm...

-- 
Kind Regards, Markus Falb