Re: RAID 5,6 sequential writing seems slower in newer kernels

[Phil Turmel <philip@turmel.org>]

On 12/02/2015 09:24 PM, Dallas Clement wrote:
> On Wed, Dec 2, 2015 at 8:18 PM, Phil Turmel <philip@turmel.org> wrote:
>> I suspect if you do a bisect on the kernel to pinpoint the change(s)
>> that is doing this, you'll find a patch that closes a device-specific or
>> filesystem sync bug or something that enables deep queues for a device.
>>
>> Modern software that needs file integrity guarantees make sparse use of
>> fdatasync and/or fsync and avoid sync entirely.  You'll have a more
>> believable test if you use fsync_on_close=1 or end_fsync=1.
>>
>> Phil
> 
> Hi Phil. Hmm that makes sense that something may have changed wrt to
> syncing.  Basically what I am trying to do with my fio testing is
> avoid any asynchronous or caching behavior.

I hope that if you really need this you are doing exhaustive testing on
failure modes -- I would be worried that these speed changes imply flaws
in the older kernels.