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Date:      Tue, 22 Sep 2015 14:43:33 -0700
From:      Chris Stankevitz <chris@stankevitz.com>
To:        Warren Block <wblock@wonkity.com>
Cc:        Matt Churchyard <matt.churchyard@userve.net>, FreeBSD FS <freebsd-fs@freebsd.org>
Subject:   Re: Name/label/id metadata: how do I make it go away
Message-ID:  <5601CB85.8070400@stankevitz.com>
In-Reply-To: <alpine.BSF.2.20.1509221500580.14674@wonkity.com>
References:  <56004C68.4020904@stankevitz.com> <alpine.BSF.2.20.1509212126470.4544@wonkity.com> <5600F0DF.8000805@stankevitz.com> <e1abb521ab324532b3445d26984f5638@SERVER.ad.usd-group.com> <5601A82A.7040304@stankevitz.com> <5601B2AF.7040306@stankevitz.com> <alpine.BSF.2.20.1509221500580.14674@wonkity.com>

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On 9/22/15 2:01 PM, Warren Block wrote:
>> According to 'geom disk list', each of my 22 drives has an "ident",
>> but only some of them have "labels".
>>
>> "ident" is turned into a "label" via a process called "tasting":
>>  sys/geom/label/g_label_disk_ident.c
>>  sys/geom/label/g_label.c
>>
>> Although it is not yet clear to me why apparently only some of my
>> disks are "tasted".
>
> Labels on devices that are mounted are "withered" and disappear.

Thank you.

Indeed when I export the pool, all of the drives become listed in 
/dev/diskid.  When I re-import the pool, some of the drives "wither" and 
are removed from /dev/diskid.  These withered drives appear as daX in 
"zpool status".  The drives that do not wither remain in /dev/diskid and 
appear in "zpool status" with their /dev/diskid/X names.

Q: Why do my identical zpool drives behave differently?

Please let me know if my hypothesis is plausible:

ZFS sees both the /dev/daX "consumers" and the /dev/diskid/X 
"providers".  ZFS is randomly selecting which to use to import the pool. 
  Sometimes it picks "consumers" and sometimes "providers".

When ZFS picks a consumer, the provider is withered away.  When ZFS 
picks a provider, the provider remains.

And if I want to dig deeper into root cause I can ask ZFS "why do you 
sometimes select from the consumer collection and sometimes from the 
provider collection when putting a pool together".  Or if I don't want 
to dig deeper I can "deal with it" or I can disable diskid using 
kern.geom.label.disk_ident.enable

Thank you again,

Chris



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