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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu)
   Importance: Undecided => Wishlist

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https://bugs.launchpad.net/bugs/1216397

Title:
  It should be possible to ignore (skip probing) a known bad disk
  partition at boot

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  Hi all,

  I guess this isn't exactly a bug - maybe more of a wishlist; but I
  thought it'd be good to log it while I'm experiencing the problem.
  Basically, I'd like a consistent kernel interface to mark faulty
  partitions (or drives) at boot time, regardless of the kernel
  subsystem (IDE, ATA) they are attributed to - but first, here is a
  (somewhat lengthy) exposition of my problem.

  
  I have a desktop PC, which some months ago, experienced a hard disk failure - I heard a loud scratching noise during disk operation, after which the bootable hard disk partition was unusable. At the time, I had Ubuntu Lucid installed on that bootable partition. Actually handling the broken disk at this time was/is not an option for me, as it would open up a whole lotta other (unrelated) work which I have to postpone to a future date. So, I've been using this PC in the past months primarily through the use of live bootable media - booting from live USB flash thumbdrive, to be exact.

  The problem here is that, at boot, the kernel starts probing all disks
  indiscriminately. Certaing distributions on the live USB I've tried,
  like PartedMagic or SliTaz, start probing and encounter the bad
  partitions; then 4-5 loud clicks can be heard from the drive, followed
  by access error messages in the log - that takes about 20-30 secinds,
  and then the the respective kernels give up, and the boot procedure
  completes successfully. Note that these distributions will recognize
  both the bad and the healthy partitions on this drive, and I have been
  mounting and using the healthy partitions from these live USB distros
  without a problem.

  However, when I try an Ubuntu-based live USB: when the kernel
  encounters the bad partition, it starts looping and accessing the
  drive, and loud clicks (followed by access errors in logs) can be
  heard way more often; and this loop can last up to 5-10 minutes - in
  all, a rather unhealthy experience. The latest I have tried is a
  Precise 12.04 based custom distro - based on Ubuntu Mini Remix with
  few extra packages, built using `ubuntu-builder`, with the `casper`
  files transferred to USB stick, previously made bootable manually via
  `syslinux`. With this distro's boot, I waited out the 272.417 seconds
  (some 4.5 mins) where this error loop occured, and the system finally
  booted; so I could obtain the logs (/var/log/syslog &
  /var/log/boot.log), that I am attaching to this post (syslog_pc_bad_hd
  and boot_pc_bad_hd.log). Thus, we can now see the messages spit out by
  the kernel on encountering the problem:

    [  247.251272] ata5.00: failed command: READ DMA
    [  247.254158] ata5.00: cmd c8/00:08:18:01:00/00:00:00:00:00/e0 tag 0 dma 4096 in
    [  247.254160]          res 51/40:00:18:01:00/00:00:00:00:00/e0 Emask 0x9 (media error)
    [  247.259985] ata5.00: status: { DRDY ERR }
    [  247.262905] ata5.00: error: { UNC }
    [  247.288574] ata5.00: configured for UDMA/33
    [  247.291390] ata5: EH complete
    [  248.614902] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
    [  248.617781] ata5.00: BMDMA stat 0x24
    [  248.620647] ata5.00: failed command: READ DMA
    [  248.623515] ata5.00: cmd c8/00:08:18:01:00/00:00:00:00:00/e0 tag 0 dma 4096 in
    [  248.623517]          res 51/40:00:18:01:00/00:00:00:00:00/e0 Emask 0x9 (media error)
    [  248.629356] ata5.00: status: { DRDY ERR }
    [  248.632265] ata5.00: error: { UNC }
    [  248.656576] ata5.00: configured for UDMA/33
    [  248.659393] ata5: EH complete
    ...
    [  254.136571] ata5.00: configured for UDMA/33
    [  254.139458] sd 5:0:0:0: [sdb] Unhandled sense code
    [  254.142395] sd 5:0:0:0: [sdb]  Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
    [  254.145393] sd 5:0:0:0: [sdb]  Sense Key : Medium Error [current] [descriptor]
    [  254.148418] Descriptor sense data with sense descriptors (in hex):
    [  254.151422]         72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00
    [  254.154438]         00 00 01 18
    [  254.157448] sd 5:0:0:0: [sdb]  Add. Sense: Unrecovered read error - auto reallocate failed
    [  254.160556] sd 5:0:0:0: [sdb] CDB: Read(10): 28 00 00 00 01 18 00 00 08 00
    [  254.163673] end_request: I/O error, dev sdb, sector 280
    [  254.166742] Buffer I/O error on device sdb, logical block 280
    [  254.169819] Buffer I/O error on device sdb, logical block 281
    [  254.172915] Buffer I/O error on device sdb, logical block 282
    [  254.175978] Buffer I/O error on device sdb, logical block 283
    [  254.178991] Buffer I/O error on device sdb, logical block 284
    [  254.181951] Buffer I/O error on device sdb, logical block 285
    [  254.184878] Buffer I/O error on device sdb, logical block 286
    [  254.187688] Buffer I/O error on device sdb, logical block 287
    [  254.190516] ata5: EH complete

  ... and as it can be seen from the log, an access is made each second
  or so.

  Now, I cannot really tell, if in all the other previous times when
  I've seen this error, the kernel would have booted if I waited the
  faulty accesses loop out - however, the sounds made are just so
  horrible and unhealthy, I never _dared_ to wait them out previosly
  (since I eventually intend to try to clone/salvage the broken
  partition when I get the time for it).

  From the log, it's obvious that an ATA-related subsystem is the one
  handling the faulty partition; unfortunately, I couldn't really see
  what driver is at fault - until I waited out the problematic loop, and
  the OS booted, so I could issue `lsmod | grep -i ata`. When this boot
  run gave me opportunity to do so, the lsmod command revealed that the
  only matching driver is `pata_atiixp`. Note that after this error is
  waited out and the OS boots, the healthy partitions of the disk are
  visible (and probably mountable) in the OS through `sudo fdisk -l`.

  So, at this point - what I would have best liked, would be a way to
  "mark" the unhealthy partition at boot time - possibly with a boot
  parameter to the `kernel` entry in `syslinux`; such that when the
  driver encounters the bad drive, it would simply "skip" it, after the
  first faulty access - and then proceed with the boot process. I don't
  know enough technicals so I could tell whether this is
  possible/realistic, though: the log messages say the error is
  encountered on the _drive_ (sdb), not on the partition (I think it was
  sdb5, but not sure).

  At this point, I found resources like:

  http://askubuntu.com/questions/230396/can-i-prevent-an-identify-
  packet-device-command-to-a-specific-device-at-boot

  or:

    http://serverfault.com/questions/112147/tell-ubuntu-to-ignore-dead-
  hard-drive-during-booting

    > I know my secondary hard drive is bad, but I cannot take it out.
    > Every Reboot takes forever because Ubuntu tries to read from it for
    > a long time and reports errors:
    >
    > [  228.984480] sd 0:0:1:0: [sdb] Add. Sense:
    >               Unrecovered read error - auto reallocate failed
    > ...
    > Looks like there may be a way to tell udev to ignore it, though I
    > don't have access to a system right now on which to test this.
    >
    > As root, open up /etc/udev/rules.d/60-persistent-storage.rules [...]
    > Add "sdb*" to that second line, so it looks like this:
    >
    > KERNEL=="ram*|loop*|fd*|nbd*|gnbd*|dm-*|md*|sdb*", GOTO="persistent_storage_end"
    >
    > Save the file and then reboot.

  So, I tried this with the `60-persistent-storage.rules` file that
  ended up on the USB flash image - I tried these changes:

    # commenting these lines:
    ##ACTION=="add", SUBSYSTEM=="module", KERNEL=="block", ATTR{parameters/events_dfl_poll_msecs}=="0", ATTR{parameters/events_dfl_poll_msecs}="2000"
    ##ACTION=="add", ATTR{removable}=="1", ATTR{events_poll_msecs}=="-1", ATTR{events_poll_msecs}="2000"

    # adding sdb here:
    KERNEL=="fd*|mtd*|nbd*|gnbd*|btibm*|dm-*|md*|sdb*", GOTO="persistent_storage_end"

    # commenting these lines:
    ##ENV{ID_PART_ENTRY_SCHEME}=="gpt", ENV{ID_PART_ENTRY_UUID}=="?*", SYMLINK+="disk/by-partuuid/$env{ID_PART_ENTRY_UUID}"
    ##ENV{ID_PART_ENTRY_SCHEME}=="gpt", ENV{ID_PART_ENTRY_NAME}=="?*", SYMLINK+="disk/by-partlabel/$env{ID_PART_ENTRY_NAME}"

  ... and they made absolutely no difference - the same troublesome
  faulty-access loop still occurs without any changes.

  
  Then I found

    http://askubuntu.com/questions/145965/how-do-i-target-a-specific-
  driver-for-libata-kernel-parameter-modding

    > At http://www.kernel.org/doc/Documentation/kernel-parameters.txt, it states,
    >
    >     libata.force=   [LIBATA] Force configurations.  The format is comma
    >         separated list of "[ID:]VAL" where ID is
    >         PORT[.DEVICE].  PORT and DEVICE are decimal numbers
    >         matching port, link or device. [...]
    >
    > So, in my setup, it seems I need to do
    >
    > libata.force=1:1.5G,2:1.5G,3:1.5G

  So I tried appending these to the `syslinux` boot entry:

    libata.force=5.00:ign
    libata.force=5.00:norst

  ... however, they make absolutely no difference either.

  Looking further through Documentation/kernel-parameters.txt, I saw:

    > 	ide-core.nodma=	[HW] (E)IDE subsystem
    > 			Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
    > 			.vlb_clock .pci_clock .noflush .nohpa .noprobe

  ... and so I tried to add these to the `syslinux` boot entry:

    sdb=noprobe
    acpi=off noapic sdb=none

  ... and those didn't work either - apparently since this drive is not
  handled as IDE, and it's not recognized as `hd` - but as `sd` device.
  However, note that when, say, SliTaz boots, when it encounters the
  faulty drive, it spits out something like:

    hda: dma_intr: status=0x51 { DriveReady SeekCompleteError }
    hda: dma_intr: error=0x40 { UncorrectableError }, LBAsect=280, sector=280
    hda: possibly failed opcode: 0xc8
    end_request: I/O error, dev hda, sector 280
    Buffer I/O error on device hda, logical block 280

  ... so I gather that, basically:

  * the SliTaz Linux kernel (not sure with which driver) sees the drive as `hda` - while
  * the Ubuntu Linux kernel (with `pata_atiixp` driver, apparently) sees the same drive as `sdb`.

  Because of this difference, I compared the `60-persistent-
  storage.rules` from Ubuntu and SliTaz - and those differed in only
  four lines, the ones that say "commenting these lines" in my snippet
  above; needless to say, that wasn't enough to get a change in
  response.

  
  Seeing how this could be driver related, as a last resort, I thought of suppressing the `pata_atiixp` driver from loading at boot time. For this, I found the following page:

    https://help.ubuntu.com/lts/installation-guide/i386/boot-parms.html

    > You can blacklist a module using the following syntax: module_name.blacklist=yes.
    > This will cause the module to be blacklisted in /etc/modprobe.d/blacklist.local
    > both during the installation and for the installed system.

  So I decided to add `pata_atiixp.blacklist=yes` to the `syslinux` boot
  line - the whole entry being:

    label ubuntu1204mini
        kernel /ubu1204/casper/vmlinuz
        append boot=casper initrd=/ubu1204/casper/initrd.lz live-media-path=/ubu1204/casper/ ignore_uuid noplymouth pata_atiixp.blacklist=yes --

  Now, this apparently _did_ cause something - because I couldn't hear
  many faulty accesses; the boot process completed superfast in
  comparison - and the faulty disk (including its healthy partitions)
  are no longer listed by `sudo fdisk -l` after the OS boots from the
  USB thumbdrive. The logs from this will be posted as
  `syslog_pc_better` and `boot_pc_better.log`; from the syslog, it is
  notable that we see:

    [    7.559862] pata_atiixp: Unknown parameter `blacklist'

  ... so apparently the syntax I used (listed on the Ubuntu wiki) is no
  longer valid; I'm not sure if it is this, that suppressed
  `pata_atiixp` to load - but for sure, `pata_atiixp` doesn't get listed
  by `lsmod` anymore, once the OS boots. So, what I conclude - with this
  Ubuntu 12.04-based kernel:

  * I can leave the boot process as is, and use `pata_atiixp`; encounter a long loop with unhealthy sounding faulty drive accesses during boot; and have access to the healthy partitions when OS boots
  * I can change the boot process, so `pata_atiixp` is not loaded; experience a very fast boot in comparison; but not have access to the healthy partitions anymore when OS boots.

  
  And here is the crux of my wish: When a partition of a drive is broken, but the other partitions of the drive are healthy and can be used, it would be great if the user could ignore/blacklist/mark the bad partition as faulty at boot using a boot parameter, and have the kernel ignore it during boot probing: either ignore it completely (as in not attempt probe at all) - or once an error is encountered during probe, the kernel would stop probing it and exit, instead of repeatedly looping and repeating the access error.

  Now, there are obviously kernel boot parameters for that purpose for
  IDE - and maybe there are some more specific parameters I could have
  used in this ATA case of mine, but I didn't have luck in finding them
  in time. And since hard disk subsystems and drivers are an extremely
  complex area to understand, it is very difficult for me (the end user)
  to figure out what would be the appropriate boot switches (if any) per
  driver/subsystem. Thus, I would have ideally wished for a **single**
  kernel parameter, say `ignore_part`, which could be appended to kernel
  boot line, e.g. in `syslinux`:

    label ubuntu1204mini
        kernel /ubu1204/casper/vmlinuz
        append boot=casper initrd=/ubu1204/casper/initrd.lz ignore_part=UUID:"a4ae3a96..." --

  ... which would then propagate through the boot process, and reach
  any/all drivers which might handle hard disks (block devices?),
  regardless of what subsystem (IDE, ATA, SCSI) they may belong to.
  Then, if a particular driver encounters errors during probe of this
  particular device, this parameter would instruct it to stop further
  probing, and continue with the rest of the boot process - instead of
  senselessly looping in faulty accesses (which are likely to worsen the
  condition of the drive), until the rest of the kernel has a chance to
  wrestle control out of the fault, and proceed with the boot some
  minutes after.

  Now, I don't know enough about drives/block devices, to know to what
  extent is the above possible per-partition. I know that at boot start,
  labels like 'sdb' may not even be attributed to devices yet - but I
  speculate that: if the master partition record of a disk is healthy -
  then when the driver, once it encounters error on "logical block 280"
  of "sdb", _might_ be able to calculate that this block 280 is in the
  scope of partition "sdb5" or UUID:"a4ae3a96..." - and as such, could
  determine that repeating the access, in case of error for that
  location, is not worth it (and thus avoid the loop). Obviously, the
  "sdb" label may change - but given that, per OS, it seems to be
  consistent, it could simply be remembered as a parameter string during
  the boot process, to which a driver could compare the name of its
  current device once it obtains it (UUIDs would be better here, I
  guess). The user would typically boot once, note the errors and the
  name under which the fault is encountered - and then reboot, adding
  that name as a known bad partition. In any case, if it is not possible
  per-partition, I guess it should be possible to do per-drive faulty
  marking (although that would make the healthy partitions ultimately
  unavailable).

  
  Well, I believe that exhausts most of my thoughts about this - it would be nice to know, to what extent is something like this possible to implement in the current Linux architecture...

  Thanks for the attention,
  Cheers!

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