On Tue, 4 Jun 2024 10:19:59 -0600
Logan Gunthorpe [off-list ref] wrote:

On 2024-06-04 06:46, Xiao Ni wrote:

quoted

Hi Mariusz

The discard can't promise to write zero to nvme disks, right? If so,
we can't use it for resync, because it can't make sure the raid is in
sync state.  

Yes, discard requests are a best effort and the drive is free to ignore
some or all of the request. See [1] for more information from Martin
Peterson.

I think if we have a device that has a fast zero operation that we know
guarantees zeroing then the kernel's write-zeros operation should be
changed to use it. We shouldn't make fast-but-dangerous options in mdadm.

Thanks,

Logan


[1] https://lore.kernel.org/all/yq1fsgwbijv.fsf@ca-mkp.ca.oracle.com/T/#u (local)

Thanks for giving the valuable feedback. I'm not directly involved in technical
details about this implementation and in fact I didn't read the previous
discussion yet. You pointed great problem and I will make sure that it is
addressed.

I asked about mdadm API, it is despite the technical implementation.
I would like to propose one command to integrate existing way (--write-zeroes)
and potentially new way (if any other fast-initialization capability would be
safe to add).

Do you see it as right approach or we should keep them separately?

Mariusz