linux-kernel - Re: [dm-devel] [PATCH 0/6] dax poison recovery with RWF_RECOVERY

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Date:   Thu, 4 Nov 2021 18:05:37 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Jane Chu <jane.chu@...cle.com>,
        "david@...morbit.com" <david@...morbit.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "agk@...hat.com" <agk@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>
Subject: Re: [dm-devel] [PATCH 0/6] dax poison recovery with
 RWF_RECOVERY_DATA flag

On Thu, Nov 04, 2021 at 10:43:23AM -0700, Christoph Hellwig wrote:
> Well, the answer for other interfaces (at least at the gold plated
> cost option) is so strong internal CRCs that user visible bits clobbered
> by cosmic rays don't realisticly happen.  But it is a problem with the
> cheaper ones, and at least SCSI and NVMe offer the error list through
> the Get LBA status command (and I bet ATA too, but I haven't looked into
> that).  Oddly enough there has never been much interested from the
> fs community for those.

"don't realistically happen" is different when you're talking about
"doesn't happen within the warranty period of my laptop's SSD" and
"doesn't happen on my fleet of 10k servers before they're taken out of
service".  There's also a big difference in speeds between an NVMe drive
(7GB/s) and a memory device (20-50GB/s).  The UBER being talked about
when I was still at Intel was similar to / slightly better than DRAM,
but that's still several failures per year across an entire data centre
that's using pmem flat-out.