Re: [RFC PATCH] mdadm: add --fast-initialize

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Tue, 4 Jun 2024 10:19:59 -0600
Logan Gunthorpe <logang@deltatee.com> wrote:

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

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