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Date: Mon, 17 Mar 2025 23:19:31 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Keith Busch <kbusch@kernel.org>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
	Kent Overstreet <kent.overstreet@linux.dev>,
	Christoph Hellwig <hch@infradead.org>, Jens Axboe <axboe@kernel.dk>,
	linux-bcachefs@vger.kernel.org, linux-block@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 13/14] block: Allow REQ_FUA|REQ_READ
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On Mon, Mar 17, 2025 at 11:32:21AM -0600, Keith Busch wrote:
> 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?

>From the error numbers we've seen it would in fact be much more likely
to be the host or transport side.

> 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.

Exactly.  It's an writeback+invalidate+reread operation.  A great
way to slow down the read, but it's not going to help you with
data recovery.