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

On 12/02/2015 09:33 PM, Dallas Clement wrote:

I'm not sure that the sync=1 has any effect in this case where I've
got direct=1 set (for non buffered I/O).  I think the sync=1 flag only
matters for buffered I/O.  I really shouldn't be setting that flag at
all.

It's substantially different from direct=1.  O_DIRECT just bypasses the
kernel's caches.  O_SYNC flushes the file data and filesystem metadata,
and kills the device caches and queues.