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From: "Michael Kjörling" <michael@kjorling.se>
To: linux-btrfs@vger.kernel.org
Subject: Re: device delete, error removing device
Date: Tue, 23 Oct 2012 07:57:21 +0000	[thread overview]
Message-ID: <20121023075721.GB391@yeono.kjorling.se> (raw)
In-Reply-To: <20121022171809.GA25498@carfax.org.uk>

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On 22 Oct 2012 18:18 +0100, from hugo@carfax.org.uk (Hugo Mills):
>> [root@f18v ~]# btrfs device delete /dev/sdb /mnt
>> [root@f18v ~]# btrfs fi show
>> failed to read /dev/sr0
>> Label: none  uuid: 6e96a96e-3357-4f23-b064-0f0713366d45
>> 	Total devices 5 FS bytes used 7.52GB
>> 	devid    5 size 12.00GB used 4.17GB path /dev/sdf
>> 	devid    4 size 12.00GB used 4.62GB path /dev/sde
>> 	devid    3 size 3.00GB used 2.68GB path /dev/sdd
>> 	devid    2 size 3.00GB used 2.68GB path /dev/sdc
>> 	*** Some devices missing
>> 
>> However, I think that last line is a bug. When I
>> 
>> [root@f18v ~]# btrfs device delete missing /mnt
>> 
>> I get
>> 
>> [ 2152.257163] btrfs: no missing devices found to remove
>> 
>> So they're missing but not missing?
> 
>    If you run sync, or wait for 30 seconds, you'll find that fi show
> shows the correct information again -- btrfs fi show reads the
> superblocks directly, and if you run it immediately after the dev del,
> they've not been flushed back to disk yet.

That sounds like it has the potential to bite a lot of people in the
rear. Yes, 30 seconds or a sync is trivial, but only if you know about
it.

Considering that a device delete is a pretty rare but potentially
important operation, would it not be better for a sync to be done
automatically after a "device delete" command? And potentially others
in a similar vein. With an option --no-sync or similar to disable the
behavior (in the relatively unlikely situation that multiple devices
are unavailable and need to be deleted, for example).

I can definitely see the described behavior qualifying as a "WTF?"
moment.

-- 
Michael Kjörling • http://michael.kjorling.se • michael@kjorling.se
                “People who think they know everything really annoy
                those of us who know we don’t.” (Bjarne Stroustrup)

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  reply	other threads:[~2012-10-23  8:08 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-22  4:32 device delete, error removing device Chris Murphy
2012-10-22  5:04 ` dima
2012-10-22  5:30   ` Chris Murphy
2012-10-22  6:02 ` Chris Murphy
2012-10-22  9:19   ` Hugo Mills
2012-10-22 16:42     ` Chris Murphy
2012-10-22 17:04       ` Goffredo Baroncelli
2012-10-22 19:36         ` Chris Murphy
2012-10-22 19:50           ` Hugo Mills
2012-10-22 20:35             ` Goffredo Baroncelli
2012-10-22 20:46             ` Chris Murphy
2012-10-22 17:18       ` Hugo Mills
2012-10-23  7:57         ` Michael Kjörling [this message]
2012-10-23 18:10           ` Goffredo Baroncelli
2012-10-23 18:17             ` Chris Murphy
2012-10-23 19:02               ` Goffredo Baroncelli
2012-10-23 20:28                 ` Chris Murphy
2012-10-23 22:16                   ` Goffredo Baroncelli
2012-10-23 22:29                     ` Chris Murphy
2012-10-24 18:06                       ` device delete, error removing device [SOLVED] Goffredo Baroncelli
2012-10-24 19:13                         ` Chris Murphy
2012-10-24 21:30                           ` Goffredo Baroncelli
2012-10-24 21:43                             ` Chris Murphy
2012-10-25 19:26                               ` Goffredo Baroncelli
2012-10-27 18:25                                 ` device delete, error removing device Chris Murphy

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