Re: homehost and 0.90 format

[NeilBrown <neilb@suse.de>]

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On Tue, 25 Nov 2014 03:31:32 +0000 "Boylan, Ross" <Ross.Boylan@ucsf.edu>
wrote:

> Thanks; I didn't know one could do that.
> 
> But am I correct in my understanding that if 2 arrays have the same homehost they will have the same end (last half?) of the UUID?  That would mean the 2 devices I'm looking at can't have the same homehost.

Yes, that is correct.

> 
> I am able to guess the homehost for one of them using your trick; none of the possibilities have tried have matched the other.

Can't help you there, sorry.

You can always look at the content of the array, device what host it *should*
belong  to, and the assemble the array with 
  --update=homehost --homehost=real-host

to "fix" the uuid.

NeilBrown


> 
> Ross
> ________________________________________
> From: NeilBrown [neilb@suse.de]
> Sent: Monday, November 24, 2014 7:08 PM
> To: Boylan, Ross
> Cc: linux-raid@vger.kernel.org
> Subject: Re: homehost and 0.90 format
> 
> On Tue, 11 Nov 2014 03:14:34 +0000 "Boylan, Ross" <Ross.Boylan@ucsf.edu>
> wrote:
> 
> > I am trying to figure out which of my RAID devices is considered home.  I haven't switched machines, but I have several operating systems, with different hostnames, on the machine.  0.90 format metadata.
> >
> > Even 2 RAID devices created on the same OS don't seem to have any UUID in common.  i thought that the end of the UUID's would be the same.  For example, inhttp://marc.info/?l=linux-raid&m=123999237229707 Neil Brown says
> > > Note that 0.90 metadata does contain homehost information to some
> > > extent.  When homehost is set, the last few bytes of the uuid is set
> > > from a hash of the homehost name.  That makes it possible to test if a
> > > 0.90 array was created for 'this' host, but not to find out what host
> > > it was created for.
> >
> > mdadm.conf has
> > HOMEHOST <system>
> >
> > The 2 UUIDS are
> >  8691ad98:af955756:ae5efbfa:dfd20ce6
> > 6d89d3b5:19a0acce:319e1a9c:58606385
> >
> > Thanks,
> > Ross Boylan
> 
> You need to guess-and-test.
> e.g.
> 
>   mdadm --detail /dev/md7 --homehost=foo | grep UUID
> 
> If it says "(local to host foo)", then "foo" is the correct name.
> If not, then try a different name.
> 
> NeilBrown
> 
> 
> >
> > Details:
> >
> > root@wheezy4:~# mdadm --detail /dev/md7
> > /dev/md7:
> >         Version : 0.90
> >   Creation Time : Fri Oct  3 17:20:13 2014
> >      Raid Level : raid1
> >      Array Size : 48828352 (46.57 GiB 50.00 GB)
> >   Used Dev Size : 48828352 (46.57 GiB 50.00 GB)
> >    Raid Devices : 1
> >   Total Devices : 1
> > Preferred Minor : 7
> >     Persistence : Superblock is persistent
> >
> >     Update Time : Tue Nov  4 17:48:40 2014
> >           State : clean
> >  Active Devices : 1
> > Working Devices : 1
> >  Failed Devices : 0
> >   Spare Devices : 0
> >
> >            UUID : 8691ad98:af955756:ae5efbfa:dfd20ce6
> >          Events : 0.1
> >
> >     Number   Major   Minor   RaidDevice State
> >        0       8       20        0      active sync   /dev/sdb4
> > root@wheezy4:~# mdadm --detail /dev/md8
> > /dev/md8:
> >         Version : 0.90
> >   Creation Time : Tue Sep 30 13:27:56 2014
> >      Raid Level : raid1
> >      Array Size : 970702784 (925.73 GiB 994.00 GB)
> >   Used Dev Size : 970702784 (925.73 GiB 994.00 GB)
> >    Raid Devices : 2
> >   Total Devices : 1
> > Preferred Minor : 8
> >     Persistence : Superblock is persistent
> >
> >     Update Time : Mon Nov 10 18:16:11 2014
> >           State : clean, degraded
> >  Active Devices : 1
> > Working Devices : 1
> >  Failed Devices : 0
> >   Spare Devices : 0
> >
> >            UUID : 6d89d3b5:19a0acce:319e1a9c:58606385
> >          Events : 0.790792
> >
> >     Number   Major   Minor   RaidDevice State
> >        0       8       19        0      active sync   /dev/sdb3
> >        1       0        0        1      removed
> > --
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> 


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