Re: ASC/ASCQ Review
- Reply: Warner Losh : "Re: ASC/ASCQ Review"
- In reply to: Warner Losh : "Re: ASC/ASCQ Review"
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Date: Fri, 21 Jul 2023 03:18:44 UTC
On 2023-07-19 11:41, Warner Losh wrote:
> btw, it also occurs to me that if I do add a 'secondary' table, then you could
> use it to generate a unique errno and experiment
> with that w/o affecting the main code until that stuff was mature.
>
> I'm not sure I'll do that now, since I've found maybe 10 asc/ascq pairs that I'd
> like to tag as 'if trying harder, retry, otherwise fail' since re-retry needs
> have changed a lot since cam was written in the late 90s and at least some of
> the asc/ascq pairs I'm looking at haven't changed since the initial import, but
> that's based on a tiny sampling of the data I have and is preliminary at best. I
> may just change it to reflect modern usage.
Hi,
If you are looking for up-to-date [20230325] asc/ascq tables in C you could
borrow mine at https://github.com/doug-gilbert/sg3_utils in lib/sg_lib_data.c
starting at line 745 .
In testing/sg_chk_asc.c is a small test program for checking that the table in
sg_lib_data.c agrees with the file that T10 supplies:
https://www.t10.org/lists/asc-num.txt
Doug Gilbert
> On Fri, Jul 14, 2023 at 5:34 PM Warner Losh <imp@bsdimp.com
> <mailto:imp@bsdimp.com>> wrote:
>
>
>
> On Fri, Jul 14, 2023 at 12:31 PM Alan Somers <asomers@freebsd.org
> <mailto:asomers@freebsd.org>> wrote:
>
> On Fri, Jul 14, 2023 at 11:05 AM Warner Losh <imp@bsdimp.com
> <mailto:imp@bsdimp.com>> wrote:
> >
> >
> >
> > On Fri, Jul 14, 2023, 11:12 AM Alan Somers <asomers@freebsd.org
> <mailto:asomers@freebsd.org>> wrote:
> >>
> >> On Thu, Jul 13, 2023 at 12:14 PM Warner Losh <imp@bsdimp.com
> <mailto:imp@bsdimp.com>> wrote:
> >> >
> >> > Greetings,
> >> >
> >> > i've been looking closely at failed drives for $WORK lately. I've
> noticed that a lot of errors that kinda sound like fatal errors have
> SS_RDEF set on them.
> >> >
> >> > What's the process for evaluating whether those error codes are
> worth retrying. There are several errors that we seem to be seeing
> (preliminary read of the data) before the drive gives up the ghost
> altogether. For those cases, I'd like to post more specific lists.
> Should I do that here?
> >> >
> >> > Independent of that, I may want to have a more aggressive 'fail
> fast' policy than is appropriate for my work load (we have a lot of data
> that's a copy of a copy of a copy, so if we lose it, we don't care:
> we'll just delete any files we can't read and get on with life, though I
> know others will have a more conservative attitude towards data that
> might be precious and unique). I can set the number of retries lower, I
> can do some other hacks for disks that tell the disk to fail faster, but
> I think part of the solution is going to have to be failing for some
> sense-code/ASC/ASCQ tuples that we don't want to fail in upstream or the
> general case. I was thinking of identifying those and creating a 'global
> quirk table' that gets applied after the drive-specific quirk table that
> would let $WORK override the defaults, while letting others keep the
> current behavior. IMHO, it would be better to have these separate rather
> than in the global data for tracking upstream...
> >> >
> >> > Is that clear, or should I give concrete examples?
> >> >
> >> > Comments?
> >> >
> >> > Warner
> >>
> >> Basically, you want to change the retry counts for certain ASC/ASCQ
> >> codes only, on a site-by-site basis? That sounds reasonable. Would
> >> it be configurable at runtime or only at build time?
> >
> >
> > I'd like to change the default actions. But maybe we just do that for
> everyone and assume modern drives...
> >
> >> Also, I've been thinking lately that it would be real nice if READ
> >> UNRECOVERABLE could be translated to EINTEGRITY instead of EIO. That
> >> would let consumers know that retries are pointless, but that the data
> >> is probably healable.
> >
> >
> > Unlikely, unless you've tuned things to not try for long at recovery...
> >
> > But regardless... do you have a concrete example of a use case?
> There's a number of places that map any error to EIO. And I'd like a use
> case before we expand the errors the lower layers return...
> >
> > Warner
>
> My first use-case is a user-space FUSE file system. It only has
> access to errnos, not ASC/ASCQ codes. If we do as I suggest, then it
> could heal a READ UNRECOVERABLE by rewriting the sector, whereas other
> EIO errors aren't likely to be healed that way.
>
>
> Yea... but READ UNRECOVERABLE is kinda hit or miss...
>
> My second use-case is ZFS. zfsd treats checksum errors differently
> from I/O errors. A checksum error normally means that a read returned
> wrong data. But I think that READ UNRECOVERABLE should also count.
> After all, that means that the disk's media returned wrong data which
> was detected by the disk's own EDC/ECC. I've noticed that zfsd seems
> to fault disks too eagerly when their only problem is READ
> UNRECOVERABLE errors. Mapping it to EINTEGRITY, or even a new error
> code, would let zfsd be tuned better.
>
>
> EINTEGRITY would then mean two different things. UFS returns in when
> checksums fail for critical filesystem errors. I'm not saying no, per se,
> just that it conflates two different errors.
>
> I think both of these use cases would be better served by CAM's publishing
> of the errors to devctl today. Here's some example data from a system I'm
> looking at:
>
> system=CAM subsystem=periph type=timeout device=da36 serial="12345"
> cam_status="0x44b" timeout=30000 CDB="28 00 4e b7 cb a3 00 04 cc 00 "
> timestamp=1634739729.312068
> system=CAM subsystem=periph type=timeout device=da36 serial="12345"
> cam_status="0x44b" timeout=30000 CDB="28 00 20 6b d5 56 00 00 c0 00 "
> timestamp=1634739729.585541
> system=CAM subsystem=periph type=error device=da36 serial="12345"
> cam_status="0x4cc" scsi_status=2 scsi_sense="72 03 11 00" CDB="28 00 ad 1a
> 35 96 00 00 56 00 " timestamp=1641979267.469064
> system=CAM subsystem=periph type=error device=da36 serial="12345"
> cam_status="0x4cc" scsi_status=2 scsi_sense="72 03 11 00" CDB="28 00 ad 1a
> 35 96 00 01 5e 00 " timestamp=1642252539.693699
> system=CAM subsystem=periph type=error device=da39 serial="12346"
> cam_status="0x4cc" scsi_status=2 scsi_sense="72 04 02 00" CDB="2a 00 01 2b
> c8 f6 00 07 81 00 " timestamp=1669603144.090835
>
> Here we get the sense key, the asc and the ascq in the scsi_sense data (I'm
> currently looking at expanding this to the entire sense buffer, since it
> includes how hard the drive tried to read the data on media and hardware
> errors). It doesn't include nvme data, but does include ata data (I'll have
> to add that data, now that I've noticed it is missing). With the sense data
> and the CDB you know what kind of error you got, plus what block didn't
> read/write correctly. With the extended sense data, you can find out even
> more details that are sense-key dependent...
>
> So I'm unsure that trying to shoehorn our imperfect knowledge of what's
> retriable, fixable, should be written with zeros into the kernel and
> converting that to a separate errno would give good results, and tapping
> into this stream daemons that want to make more nuanced calls about disks
> might be the better way to go. One of the things I'm planning for $WORK is
> to enable the retry time limit of one of the mode pages so that we fail
> faster and can just delete the file with the 'bad' block that we'd get
> eventually if we allowed the full, default error processing to run, but that
> 'slow path' processing kills performance for all other users of the
> drive... I'm unsure how well that will work out (and I know I'm lucky that
> I can always recover any data for my application since it's just a cache).
>
> I'd be interested to hear what others have to say here thought, since my
> focus on this data is through the lense of my rather specialized application...
>
> Warner
>
> P.S. That was generated with this rule if you wanted to play with it...
> You'd have to translate absolute disk blocks to a partition and an offset
> into the filesystem, then give the filesystem a chance to tell you what of
> its data/metadata that block is used for...
>
> # Disk errors
> notify 10 {
> match "system" "CAM";
> match "subsystem" "periph";
> match "device" "[an]?da[0-9]+";
> action "logger -t diskerr -p daemon.info <http://daemon.info> $_
> timestamp=$timestamp";
> };
>