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

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...