From: Gionatan Danti <g.danti@assyoma.it>
To: LVM general discussion and development <linux-lvm@redhat.com>,
Zdenek Kabelac <zkabelac@redhat.com>
Cc: Joe Thornber <thornber@redhat.com>
Subject: Re: [linux-lvm] Snapshot behavior on classic LVM vs ThinLVM
Date: Sun, 14 May 2017 22:39:21 +0200 [thread overview]
Message-ID: <b0e4f2d1cfca0ea32da27b1cb34bf1be@assyoma.it> (raw)
In-Reply-To: <20170512134157.GA2523@nim>
Il 12-05-2017 15:42 Joe Thornber ha scritto:
> On Fri, May 12, 2017 at 03:02:58PM +0200, Gionatan Danti wrote:
>> On 02/05/2017 13:00, Gionatan Danti wrote:
>> >>Anyway, I think (and maybe I am wrong...) that the better solution is to
>> >>fail *all* writes to a full pool, even the ones directed to allocated
>> >>space. This will effectively "freeze" the pool and avoid any
>> >>long-standing inconsistencies.
>
> I think dm-thin behaviour is fine given the semantics of write
> and flush IOs.
>
> A block device can complete a write even if it hasn't hit the physical
> media, a flush request needs to come in at a later time which means
> 'flush all IOs that you've previously completed'. So any software
> using
> a block device (fs, database etc), tends to generate batches of writes,
> followed by a flush to commit the changes. For example if there was a
> power failure between the batch of write io completing and the flush
> completing you do not know how much of the writes will be visible when
> the machine comes back.
>
> When a pool is full it will allow writes to provisioned areas of a thin
> to
> succeed. But if any writes failed due to inability to provision then a
> REQ_FLUSH io to that thin device will *not* succeed.
>
> - Joe
True, but the real problem is that most of the failed flushes will *not*
bring the filesystem read-only, as both ext4 and xfs seems to go
read-only only when *metadata* updates fail. As this very same list
recommend using ext4 with errors=remount-ro on the basis that putting
the filesystem in a read-only state after any error I the right thing, I
was somewhat alarmed to find that, as far I can tell, ext4 goes
read-only on metadata errors only.
So, let me reiterate: can we consider thinlvm + xfs as safe as thinlvm +
ext4 + errors=remount-ro?
Thanks.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
next prev parent reply other threads:[~2017-05-14 20:39 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-06 14:31 [linux-lvm] Snapshot behavior on classic LVM vs ThinLVM Gionatan Danti
2017-04-07 8:19 ` Mark Mielke
2017-04-07 9:12 ` Gionatan Danti
2017-04-07 13:50 ` L A Walsh
2017-04-07 16:33 ` Gionatan Danti
2017-04-13 12:59 ` Stuart Gathman
2017-04-13 13:52 ` Xen
2017-04-13 14:33 ` Zdenek Kabelac
2017-04-13 14:47 ` Xen
2017-04-13 15:29 ` Stuart Gathman
2017-04-13 15:43 ` Xen
2017-04-13 17:26 ` Stuart D. Gathman
2017-04-13 17:32 ` Stuart D. Gathman
2017-04-14 15:17 ` Xen
2017-04-14 7:27 ` Gionatan Danti
2017-04-14 7:23 ` Gionatan Danti
2017-04-14 15:23 ` Xen
2017-04-14 15:53 ` Gionatan Danti
2017-04-14 16:08 ` Stuart Gathman
2017-04-14 17:36 ` Xen
2017-04-14 18:59 ` Gionatan Danti
2017-04-14 19:20 ` Xen
2017-04-15 8:27 ` Xen
2017-04-15 23:35 ` Xen
2017-04-17 12:33 ` Xen
2017-04-15 21:22 ` Xen
2017-04-15 21:49 ` Xen
2017-04-15 21:48 ` Xen
2017-04-18 10:17 ` Zdenek Kabelac
2017-04-18 13:23 ` Gionatan Danti
2017-04-18 14:32 ` Stuart D. Gathman
2017-04-19 7:22 ` Xen
2017-04-07 22:24 ` Mark Mielke
2017-04-08 11:56 ` Gionatan Danti
2017-04-07 18:21 ` Tomas Dalebjörk
2017-04-13 10:20 ` Gionatan Danti
2017-04-13 12:41 ` Xen
2017-04-14 7:20 ` Gionatan Danti
2017-04-14 8:24 ` Zdenek Kabelac
2017-04-14 9:07 ` Gionatan Danti
2017-04-14 9:37 ` Zdenek Kabelac
2017-04-14 9:55 ` Gionatan Danti
2017-04-22 7:14 ` Gionatan Danti
2017-04-22 16:32 ` Xen
2017-04-22 20:58 ` Gionatan Danti
2017-04-22 21:17 ` Zdenek Kabelac
2017-04-23 5:29 ` Xen
2017-04-23 9:26 ` Zdenek Kabelac
2017-04-24 21:02 ` Xen
2017-04-24 21:59 ` Zdenek Kabelac
2017-04-26 7:26 ` Gionatan Danti
2017-04-26 7:42 ` Zdenek Kabelac
2017-04-26 8:10 ` Gionatan Danti
2017-04-26 11:23 ` Zdenek Kabelac
2017-04-26 13:37 ` Gionatan Danti
2017-04-26 14:33 ` Zdenek Kabelac
2017-04-26 16:37 ` Gionatan Danti
2017-04-26 18:32 ` Stuart Gathman
2017-04-26 19:24 ` Stuart Gathman
2017-05-02 11:00 ` Gionatan Danti
2017-05-12 13:02 ` Gionatan Danti
2017-05-12 13:42 ` Joe Thornber
2017-05-14 20:39 ` Gionatan Danti [this message]
2017-05-15 12:50 ` Zdenek Kabelac
2017-05-15 14:48 ` Gionatan Danti
2017-05-15 15:33 ` Zdenek Kabelac
2017-05-16 7:53 ` Gionatan Danti
2017-05-16 10:54 ` Zdenek Kabelac
2017-05-16 13:38 ` Gionatan Danti
2018-02-27 18:39 ` Xen
2018-02-28 9:26 ` Zdenek Kabelac
2018-02-28 19:07 ` Gionatan Danti
2018-02-28 21:43 ` Zdenek Kabelac
2018-03-01 7:14 ` Gionatan Danti
2018-03-01 8:31 ` Zdenek Kabelac
2018-03-01 9:43 ` Gianluca Cecchi
2018-03-01 11:10 ` Zdenek Kabelac
2018-03-01 9:52 ` Gionatan Danti
2018-03-01 11:23 ` Zdenek Kabelac
2018-03-01 12:48 ` Gionatan Danti
2018-03-01 16:00 ` Zdenek Kabelac
2018-03-01 16:26 ` Gionatan Danti
2018-03-03 18:32 ` Xen
2018-03-04 20:34 ` Zdenek Kabelac
2018-03-03 18:17 ` Xen
2018-03-04 20:53 ` Zdenek Kabelac
2018-03-05 9:42 ` Gionatan Danti
2018-03-05 10:18 ` Zdenek Kabelac
2018-03-05 14:27 ` Gionatan Danti
2018-03-03 17:52 ` Xen
2018-03-04 23:27 ` Zdenek Kabelac
2017-04-22 21:22 ` Zdenek Kabelac
2017-04-24 13:49 ` Gionatan Danti
2017-04-24 14:48 ` Zdenek Kabelac
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