[LSF/MM TOPIC][LSF/MM ATTEND] OCSSDs - SMR, Hierarchical Interface, and Vector I/Os

[Damien Le Moal]

Matias,

On 1/10/17 22:06, Matias Bjorling wrote:
> On 01/10/2017 05:24 AM, Theodore Ts'o wrote:
>> This may be an area where if we can create the right framework, and
>> fund some research work, we might be able to get some researchers and
>> their graduate students interested in doing some work in figuring out
>> what sort of divisions of responsibilities and hints back and forth
>> between the storage device and host have the most benefit.
>>
> 
> That is a good idea. There is a couple of papers at FAST with
> Open-Channel SSDs this year.  They look into the interface and various
> ways to reduce latency fluctuations.
> 
> One thing I've heard a couple of times is the feature to move the GC
> read/write process into the firmware. Enabling the host to offload GC
> data movement, while the keeping the host in control. Would this be
> beneficial for SMR?

Host-aware SMR drives already have GC internally implemented (for cases
when the host does not write sequentially). Host-managed drives do not.
As for moving an application specific GC code into the device, well,
code injection in the storage device is not for tomorrow, and likely not
ever.

There are however other clever ways to reduce GC related host overhead
with basic commands. For SCSI, these may be WRITE SCATTERED, EXTENDED
COPY, and some others can greatly improve overhead over a simple
read+write loop. A better approach to GC offload may not be a "GC"
command, but something more generic for moving around LBAs internally
within the device. That is, if existing commands are not satisfactory.

Best.

-- 
Damien Le Moal, Ph.D.
Sr. Manager, System Software Research Group,
Western Digital Corporation
Damien.LeMoal at wdc.com
(+81) 0466-98-3593 (ext. 513593)
1 kirihara-cho, Fujisawa,
Kanagawa, 252-0888 Japan
www.wdc.com, www.hgst.com