From: Zdenek Kabelac <zkabelac@redhat.com>
To: Gionatan Danti <g.danti@assyoma.it>
Cc: Xen <list@xenhideout.nl>,
LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Snapshot behavior on classic LVM vs ThinLVM
Date: Thu, 1 Mar 2018 09:31:02 +0100 [thread overview]
Message-ID: <c5f98473-1dad-b48e-ef3f-b311e5de2ee9@redhat.com> (raw)
In-Reply-To: <0a322a6f355a0744427f2a7a45162c81@assyoma.it>
Dne 1.3.2018 v 08:14 Gionatan Danti napsal(a):
> Il 28-02-2018 22:43 Zdenek Kabelac ha scritto:
>> On default - full pool starts to 'error' all 'writes' in 60 seconds.
>
> Based on what I remember, and what you wrote below, I think "all writes" in
> the context above means "writes to unallocated areas", right? Because even
> full pool can write to already-provisioned areas.
yes
>
>> The main problem is - after reboot - this 'missing/unprovisioned'
>> space may provide some old data...
>
> Can you elaborate on this point? Are you referring to current behavior or to
> an hypothetical "full read-only" mode?
If the tool wanted to write 1sector to 256K chunk that needed provisioning,
and provisioning was not possible - after reboot - you will still see
the 'old' content.
In case of filesystem, that does not stop upon 1st. failing write you then can
see a potential problem since fs could issue writes - where halve of them
were possibly written and other halve was errored - then you reboot,
and that 'error' halve is actually returning 'some old data' and this can make
filesystem seriously confused...
Fortunately both ext4 & xfs both have now correct logic here for journaling,
although IMHO still not optimal.
> True, but this not disprove the main point: snapshots are a invaluable tool in
> building your backup strategy. Obviously, if thin-pool meta volume has a
> problem, than all volumes (snapshot or not) become invalid. Do you have any
> recovery strategy in this case? For example, the root ZFS uberblock is written
> on *both* device start and end. Does something similar exists for thinp?
Unfortunately losing root blocks on thin-pool metadata is a big problem.
That's why metadata should be rather on some resilient fast storage.
Logic of writing should not let data corrupt (% broken kernel).
But yes - there is quite some room for improvement in thin_repair tool....
>> There are also some on going ideas/projects - one of them was to have
>> thinLVs with priority to be always fully provisioned - so such thinLV
>> could never be the one to have unprovisioned chunks....
>> Other was a better integration of filesystem with 'provisioned' volumes.
>
> Interesting. Can you provide some more information on these projects?
Likely watching Joe's pages (main thin-pool creator) and whatever XFS groups
is working on....
Also note - we are going to integrate VDO support - which will be a 2nd. way
for thin-provisioning with different set of features - missing snapshots, but
having compression & deduplication....
Regards
Zdenek
next prev parent reply other threads:[~2018-03-01 8:31 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
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 [this message]
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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