Re: [PATCH v5 2/2] Add support for SCT Write Same

[Tom Yan]

On 11 August 2016 at 09:47, Martin K. Petersen
<martin.petersen@xxxxxxxxxx> wrote:
>
> Tom> so we can at most allow only a 2-block (well, or 3-block) payload.
>
> We tried turning on multi block payloads and it was a massive disaster.
> Many drives reported that they supported 8 block payloads but actually
> didn't. Instead of playing the blacklist game we capped it at a single
> sector.

I don't know, apparently Windows does multi block payloads though (at
least that's how it advertise on the simulated VPD).

What I meant was it will not make a big difference in our case anyway.
Given the 32-bit representation limitation, we could be at best using
a full 2-block payload. So let's not do 2 but 1? Fine :P

>
> Many drives from different vendors were affected by this. So we'd have
> to make multi block payloads an explicit opt-in like we did for
> discard_zeroes_data. However, given that "big" discards are mainly done
> synchronously when creating filesystems, I am not sure there is any real
> benefit to this.
>

Probably. Perhaps it could make a difference upon deletion of some
really big files (though the logical sectors used may not be
continuous anyway).

> --
> Martin K. Petersen      Oracle Linux Engineering