On 21/01/2021 20.49, Heiner Litz wrote:
there are a couple more, but again I would understand if those are
deemed not important enough to keep it.
device emulation of (non-ZNS) SSD block device
That'll soon be available. We will be open-sourcing a new device mapper
(dm-zap), which implements an indirection layer that enables ZNS SSDs to
be exposed as a conventional block device.
die control: yes endurance groups would help but I am not aware of any
vendor supporting it
It is out there. Although, is this still important in 2021? OCSSD was
made back in the days where media program/erase suspend wasn't commonly
available and SSD controller were more simple. With today's media and
SSD controllers, it is hard to compete without leaving media throughput
on the table. If needed, splitting a drive into a few partitions should
be sufficient for many many types of workloads.
finer-grained control: 1000's of open blocks vs. a handful of
concurrently open zones
It is dependent on the implementation - ZNS SSDs also supports 1000's of
open zones.
Wrt to available OCSSD hardware - there isn't, to my knowledge, proper
implementations available, where media reliability is taken into account.
Generally for the OCSSD hardware implementations, their UBER is
extremely low, and as such RAID or similar schemes must be implemented
on the host. pblk does not implement this, so at best, one should not
store data if one wants to get it back at some point. It also makes for
an unfair SSD comparison, as there is much more to an SSD than what
OCSSD + pblk implements. At worst, it'll lead to false understanding of
the challenges of making SSDs, and at best, work can be used as the
foundation for doing an actual SSD implementation.
OOB area: helpful for L2P recovery
It is known as LBA metadata in NVMe. It is commonly available in many of
today's SSD.
I understand your point that there is a lot of flexibility, but my
counter point is that there isn't anything in OCSSD, that is not
implementable or commonly available using today's NVMe concepts.
Furthermore, the known OCSSD research platforms can easily be updated to
expose the OCSSD characteristics through standardized NVMe concepts.
That would probably make for a good research paper.
