Re: [PATCH 13/14] block: Allow REQ_FUA|REQ_READ

Keith Busch
2025-03-17T17:32:24Z

On Mon, Mar 17, 2025 at 11:30:13AM -0400, Martin K. Petersen wrote:
> Kent is trying to address a scenario in which data in the cache is
> imperfect and the data on media is reliable. SCSI did not consider such
> a scenario because the entire access model would be fundamentally broken
> if cache contents couldn't be trusted.

I'm not even sure it makes sense to suspect the controller side, but the
host side is considered reliable? If the media is in fact perfect, and
if non-FUA read returns data that fails the checksum, wouldn't it be
just as likely that the transport or host side is the problem? Every
NVMe SSD I've developered couldn't efficiently fill the PCIe tx-buffer
directly from media (excluding Optane; RIP), so a read with or without
FUA would stage the data in the very same controller-side DRAM.