On Fri Oct 31, 2014 at 04:19:04PM +0100, Caspar Smit wrote:

Hi all,

I'm trying to get the POLICY framework of mdadm working but I can't seem to.

As i understand in the man page of mdadm the Incremental and POLICY
directives could allow adding a new disk without MD superblock as
spare to an already active array:

"Note that mdadm will normally only add devices to an array which were
previously working (active or spare) parts of that array.  The support
for automatic inclusion of a new drive as a spare in some array
requires a configuration through POLICY in config file."

Furthermore:

"If no md metadata is found, the device may be still added to an array
as a spare if POLICY allows."


To get the basics working I created a system with 3 disks /dev/sdb,
/dev/sdc and /dev/sdd

Created a RAID5 with one missing disk:

mdadm -C /dev/md0 -l 5 -n 3 /dev/sd[b-c] missing

I set the POLICY in mdadm.conf to:

POLICY action=force-spare

This should add any device (passed through mdadm --incremental) as
spare no matter what (Am i correct?)

Now when I do:

#mdadm --incremental /dev/sdd
mdadm: no RAID superblock on /dev/sdd.

Well, i know there is no MD superblock on /dev/sdd but shouldn't the
policy setting kick in here and add /dev/sdd as spare (and hence start
rebuilding) to /dev/md0?

mdadm version: 3.2.5-5 (latest debian wheezy stable)
kernel version: 3.2.63-2 (latest debian wheezy stable)

According to the mdadm.conf manual page on my machine:
      The  action  item  determines the automatic behavior allowed for
      devices matching the path and type  in  the  same  line.  If  a
      device  matches  several  lines  with different actions then the
      most permissive will apply. The  ordering  of  policy lines  is
      irrelevant to the end result.

With the examples given being:
      POLICY domain=domain1 metadata=imsm path=pci-0000:00:1f.2-scsi-* action=spare
      POLICY domain=domain1 metadata=imsm path=pci-0000:04:00.0-scsi-[01]* action=include

So I'd guess that the path= entry is required (though the type value
would look to be optional, which is not clear from the text).

HTH,
    Robin
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