From mboxrd@z Thu Jan  1 00:00:00 1970
From: "John Stoffel" <john@stoffel.org>
Subject: Re: Possible bug in mirror target
Date: Sun, 10 Feb 2019 16:58:06 -0500
Message-ID: <23648.40558.660430.523285@quad.stoffel.home>
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To: Zdenek Kabelac <zkabelac@redhat.com>
Cc: dm-devel@redhat.com, Drew Hastings <dhastings@crucialwebhost.com>
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>>>>> "Zdenek" =3D=3D Zdenek Kabelac <zkabelac@redhat.com> writes:

Zdenek> Dne 05. 02. 19 v 1:47 Drew Hastings napsal(a):
>> Hi,
>> =

>> I'm assuming all user space code is expected to use the handle_errors fe=
ature, =

>> so this isn't that big of a deal. I'm also using 4.19.13, which I think =
is =

>> more recent than the latest update to=A0dm-raid1.c
>> =

>> That said, there may be a bug that causes the entire mirror to crash if =
there =

>> is an error on the first leg of the mirror, but not on the 2nd leg.
>> =

>> Works fine if you do cause IO errors on the 2nd leg:
>> =

>> root@kernel-dev:~# dmsetup create zerodev --table "0 1073741824 zero"
>> root@kernel-dev:~# dmsetup create errordev --table "0 1073741824 error"
>> =

>> =

>> root@kernel-dev:~# dmsetup create mirror-table --table "0 1073741824 mir=
ror =

>> core 2 524288 nosync 2 /dev/mapper/zerodev 0 /dev/mapper/errordev 0 0"

Zdenek> There are 2 operational modes for old dm mirror target.
Zdenek> One requires to handle errors externally. Please check i.e. the fol=
lowing =

Zdenek> guide for mirror target:

Zdenek> https://wiki.gentoo.org/wiki/Device-mapper

Zdenek> Lvm2 is using 'dmeventd' to service this error handling
Zdenek> (i.e. dropping the mirror leg or allocating replacement one).

Is it time to remove the dm-mirror target then?  Or to deprecate it?
Or to just silently replace it with something that does the right
thing when errors happen?  I can't think of why *anyone* would want to
use the dm-mirror target as it now seems to work.

John