[ ... ] sync=1 really differentiates drives and you really
find which drives are better. [ ... ]
It is not necessarily "better" in a strict sense: flash SSD
devices with supercapacitor-backed persistent caches can be much
faster on 'fsync' heavy workloads, but also cost a lot more
(probably mostly because of market segmentation). Of course
especially on a RAID5 set with lots of read-modify-write.
It is a different performance envelope, not necessarily a
"better" one. If one does not need small-write speed then
cheaper drivers are more appropriate.
However devices which don't have persistent caches and still
have high 'sync=1'/'direct=1' speed because they don't implement
'fsync' synchronously are definitely worse, in the sense of
having arguably no performance at all.
Some manufacturers think that using an SLC cache helps without a
persistent-ed RAM cache, but the persistent=-ed RAM seems a lot
better to me.