[PATCH V9 4/9] nvmet: add ZBD over ZNS backend support

[Damien Le Moal]

On 2021/01/19 3:25, Christoph Hellwig wrote:
> On Tue, Jan 12, 2021 at 07:52:27AM +0000, Damien Le Moal wrote:
>>>
>>> I do not understand the logic here, given that NVMe does not have
>>> conventional zones.
>>
>> 512e SAS & SATA SMR drives (512B logical, 4K physical) are a big thing, and for
>> these, all writes in sequential zones must be 4K aligned. So I suggested to
>> Chaitanya to simply use the physical block size as the LBA size for the target
>> to avoid weird IO errors that would not make sense in ZNS/NVMe world (e.g. 512B
>> aligned write requests failing).
> 
> But in NVMe the physical block size exposes the atomic write unit, which
> could be way too large.  Іf we want to do this cleanly we need to expose
> a minimum sequential zone write alignment value in the block layer.
> 

OK, good point. I think I can cook something like that today.

-- 
Damien Le Moal
Western Digital Research