On 08/11/2017 12:16 PM, Chris Murphy wrote:
On Fri, Aug 11, 2017 at 7:53 AM, Robert Nichols
<rnicholsnos...@comcast.net> wrote:
On 08/10/2017 11:06 AM, Chris Murphy wrote:


On Thu, Aug 10, 2017, 6:48 AM Robert Moskowitz <r...@htt-consult.com>
wrote:



On 08/09/2017 10:46 AM, Chris Murphy wrote:

If it's a bad sector problem, you'd write to sector 17066160 and see if

the

drive complies or spits back a write error. It looks like a bad sector
in
that the same LBA is reported each time but I've only ever seen this
with
both a read error and a UNC error. So I'm not sure it's a bad sector.

What is DID_BAD_TARGET?


I have no experience on how to force a write to a specific sector and
not cause other problems.  I suspect that this sector is in the /
partition:

Disk /dev/sda: 240.1 GB, 240057409536 bytes, 468862128 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0000c89d

      Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048     2099199     1048576   83  Linux
/dev/sda2         2099200     4196351     1048576   82  Linux swap /
Solaris
/dev/sda3         4196352   468862127   232332888   83  Linux


LBA 17066160 would be on sda3.

dd if=/dev/sda skip=17066160 count=1 2>/dev/null | hexdump -C

That'll read that sector and display hex and ascii. If you recognize the
contents, it's probably user data. Otherwise, it's file system metadata or
a system binary.

If you get nothing but an I/O error, then it's lost so it doesn't matter
what it is, you can definitely overwrite it.

dd if=/dev/zero of=/dev/sda seek=17066160 count=1


You really don't want to do that without first finding out what file is
using
that block. You will convert a detected I/O error into silent corruption of
that file, and that is a much worse situation.

Yeah he'd want to do an fsck -f and see if repairs are made, and also
rpm -Va. There *will* be legitimately modified files, so it's going to
be tedious to exactly sort out the ones that are legitimately modified
vs corrupt. If it's a configuration file, I'd say you could ignore it
but any modified binaries other than permissions need to be replaced
and is the likely culprit.

The smartmontools page has hints on how to figure out what file is
affected by a particular sector being corrupt but the more layers are
involved the more difficult that gets. I'm not sure there's an easy to
do this with LVM in between the physical device and file system.

fsck checks filesystem metadata, not the content of files. It is not going
to detect that a file has had 512 bytes replaced by zeros. If the file
is a non-configuration file installed from an RPM, then "rpm -Va" should
flag it.

LVM certainly makes the procedure harder. Figuring out what filesystem
block corresponds to that LBA is still possible, but you have to examine
the LV layout in /etc/lvm/backup/ and learn more than you probably wanted
to know about LVM.

--
Bob Nichols     "NOSPAM" is really part of my email address.
                Do NOT delete it.

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