On 01/28/2013 09:33 AM, Theo Cabrerizo Diem wrote:

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Is there a way that I could flag the raid device (or the partitions)
to not be auto-detected on boot ? I'm afraid that since the "mdadm
--create --assume-clean" completed successfuly before, a reboot on
this machine might bring the array fully online and, for example,
might trigger a check or resync of data. That would be the worse case.

You would modify your mdadm.conf file per its man-page to not allow
automatic assembly, then update your initramfs.  Both of these tasks
vary by distro.

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quoted

So your copy of mdadm is very new, and has the new defaults for data
offset (leaving more room for a bad block log).  You need to boot with a
slightly older liveCD or other rescue media to get a copy of mdadm that
is about 1 year old.  Re-run the "mdadm --create --assume-clean" with
that version of mdadm.

(The development version of mdadm has command-line syntax to set the
data offset per device, but I don't believe it has been released yet.
If you are comfortable using git and compiling your own utility, that
would be another option.)

I have no problem compiling the tools myself. I would actually prefer
that than triggering a reboot on the machine and having unpredictable
results from how it would be detected after the multiple attempts to
create the device.

Is only the userspace tool required for this update or should I build
also the kernel module too ?

Just the userspace tool.

Is there any means that would prevent the "mdadm --scan ..." usually
on ramdisks or init scripts for touching my array ? (i.e changing the
partition types, for example ? )

Just the mdadm.conf file that ends up in the initramfs.

I'm using WD Caviar Green disks, which are "cheap desktop drives" :).
It is a home setup after all :( . I did got some WD "Red" series which
supposedly have a "NAS friendly" firmware. Will gladly report back if
those support SCTERC. They are less than 10% more expensive nowadays
than the "Green" series.

Yes, the Red drives are reported to support SCTERC.  You could modify
the script to cover both cases:

#! /bin/bash
# Place in rc.local or wherever your distro expects boot-time scripts
#
for x in sdg sdh sdi sdj
do
    smartctl -l scterc,70,70 /dev/$x &>/dev/null || \
    echo 180 >/sys/block/$x/device/timeout
done

Drives that don't accept the seven-second timeout will be given a long
driver timeout.

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Once all this is solved, I would be more than happy to submit changes
to the current wiki page containing the additional information you
have been providing me that doesn't exists there, including pushing
the timeout to a long one.

Please do.  And also strongly recommend people ask for help on this list
if they are the least bit hesitant.

Phil