Re: Trying to get POLICY working

[NeilBrown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 3106 bytes --]

On Sat, 1 Nov 2014 11:20:01 +1100 NeilBrown <neilb@suse.de> wrote:

> On Fri, 31 Oct 2014 16:19:04 +0100 Caspar Smit <c.smit@truebit.nl> 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.

Actually, don't bother.  I must have been asleep.

Your problem is that you haven't defined a 'domain'.
A new spare needs to be assigned to a 'domain', and it will be attached to
any array in the same domain, as needed.

You can give all devices the domain "default" with

   POLICY domain=default

The domain of an array is inherited from the member devices, or can be set
with "spare-group=" in mdadm.conf.

So

   POLICY domain=default action=force-spare

should make it work for you.

NeilBrown

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 828 bytes --]