On 10/25/2016 05:42 PM, Gandalf Corvotempesta wrote:
2016-10-24 16:13 GMT+02:00 Niels de Vos <ndevos@xxxxxxxxxx>:
Yes, correct. But note that different filesystems can handle bad sectors
differently, read-only filesystems is the most common default though.
In 'man 8 mount' the option "errors=" describes the different values for
ext2/3/4. Configuring it to "continue" will most likely cause data
corruption or other bad problems and is definitely not advised ;-)
From the opennebula forum:
"I think your notion of kernel behaviour during disk failures is not
correct. First of all, this is heavily filesystem dependent. Moreover,
when the bad sector is in the file data (as opposed to filesystem
metadata), read(2)returns something like ENXIO, and the filesystem
continues operating. When the bad sector is in the filesystem
metadata, most filesystems remount themselves read-only (AFAIK with
ext*fs, the exact behaviour can be set via tune2fs(8) as "remount
r/only", "panic", and "ignore" for the brave :-). When the disk is bad
to the point of generating unplug/replug sequence (e.g. SATA channel
reset), the filesystem starts returning ENXIO for all operations, but
it is still mounted. For systemd-based distributions, systemd
sometimes detects an unplugged disk (if it is mounted via /etc/fstab
entry), and umount(2)s it.
The kernel itself does not disable the disk, nor it remounts it r/only
in response to all types of failure."
so, how gluster handle a ENXIO ?
There is no special handling for specific errors.
i) If a particular syscall fails in the brick process, the errno is
propagated back to the application.
ii) If the posix health-checker thread [1], which runs
periodically,fails in its
I/O, it kills the brick process, subsequent to which any I/O on that
brick will
fail with ENOTCONN.
-Ravi
[1]
https://github.com/gluster/glusterfs/blob/v3.8.5/xlators/storage/posix/src/posix-helpers.c#L1809
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