Re: [PATCH v5] lightnvm: physical block device (pblk) target

[Matias BjÃrling]

On 04/11/2017 04:31 PM, Javier GonzÃlez wrote:
> This patch introduces pblk, a host-side translation layer for
> Open-Channel SSDs to expose them like block devices. The translation
> layer allows data placement decisions, and I/O scheduling to be
> managed by the host, enabling users to optimize the SSD for their
> specific workloads.
>
> An open-channel SSD has a set of LUNs (parallel units) and a
> collection of blocks. Each block can be read in any order, but
> writes must be sequential. Writes may also fail, and if a block
> requires it, must also be reset before new writes can be
> applied.
>
> To manage the constraints, pblk maintains a logical to
> physical address (L2P) table,  write cache, garbage
> collection logic, recovery scheme, and logic to rate-limit
> user I/Os versus garbage collection I/Os.
>
> The L2P table is fully-associative and manages sectors at a
> 4KB granularity. Pblk stores the L2P table in two places, in
> the out-of-band area of the media and on the last page of a
> line. In the cause of a power failure, pblk will perform a
> scan to recover the L2P table.
>
> The user data is organized into lines. A line is data
> striped across blocks and LUNs. The lines enable the host to
> reduce the amount of metadata to maintain besides the user
> data and makes it easier to implement RAID or erasure coding
> in the future.
>
> pblk implements multi-tenant support and can be instantiated
> multiple times on the same drive. Each instance owns a
> portion of the SSD - both regarding I/O bandwidth and
> capacity - providing I/O isolation for each case.
>
> Finally, pblk also exposes a sysfs interface that allows
> user-space to peek into the internals of pblk. The interface
> is available at /dev/block/*/pblk/ where * is the block
> device name exposed.
>
> This work also contains contributions from:
>   Matias BjÃrling <matias@xxxxxxxxxxxx>
>   Simon A. F. Lund <slund@xxxxxxxxxxxx>
>   Young Tack Jin <youngtack.jin@xxxxxxxxx>
>   Huaicheng Li <huaicheng@xxxxxxxxxxxxxxx>
>
> Signed-off-by: Javier GonzÃlez <javier@xxxxxxxxxxxx>

Awesome. Applied for 4.12.