On Fri, 31 Oct 2014 16:19:04 +0100 Caspar Smit <c.smit@xxxxxxxxxx> 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?)
That is the theory, yes.
>
> Now when I do:
>
> #mdadm --incremental /dev/sdd
> mdadm: no RAID superblock on /dev/sdd.
The message suggests that 'guess_super' found something on the device, but
it didn't turn out to be something useful.... not very helpful I know.
What does "mdadm --examine /dev/sdd" report?
I suspect there is a partition table and that is causing the confusion.
Try removing the partition table (dd /dev/zero to the device for a few K).
Then try again.
Probably need a fix like:
diff --git a/Incremental.c b/Incremental.c
index c9372587f518..3156190c4603 100644
--- a/Incremental.c
+++ b/Incremental.c
@@ -196,7 +196,7 @@ int Incremental(struct mddev_dev *devlist, struct context *c,
policy = disk_policy(&dinfo);
have_target = policy_check_path(&dinfo, &target_array);
- if (st == NULL && (st = guess_super(dfd)) == NULL) {
+ if (st == NULL && (st = guess_super_type(dfd, guess_array)) == NULL) {
if (c->verbose >= 0)
pr_err("no recognisable superblock on %s.\n",
devname);
and probably should improve the error messages...
Thanks for the report. Please let me know if that works, and what other
difficulties you hit.
Thanks,
NeilBrown
>
> 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)
>
> Kind regards,
> Caspar Smit
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