From: Gionatan Danti <g.danti@assyoma.it>
To: Zdenek Kabelac <zkabelac@redhat.com>
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, 01 Mar 2018 08:14:14 +0100 [thread overview]
Message-ID: <0a322a6f355a0744427f2a7a45162c81@assyoma.it> (raw)
In-Reply-To: <eea26091-40e7-8f31-e4ba-dfab059f3d70@redhat.com>
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.
> 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?
> It still depends - there is always some sort of 'race' - unless you
> are willing to 'give-up' too early to be always sure, considering
> there are technologies that may write many GB/s...
Sure - this was the "more-or-less" part in my sentence.
> You can use rootfs with thinp - it's very fast for testing i.e.
> upgrades
> and quickly revert back - just there should be enough free space.
For testing, sure. However for a production machine I would rarely use
root on thinp. Maybe my reasoning is skewed by the fact that I mostly
work with virtual machines, so test/heavy upgrades are *not* done on the
host itself, rather on the guest VM.
>
> Depends on version of kernel and filesystem in use.
>
> Note RHEL/Centos kernel has lots of backport even when it's look quite
> old.
Sure, and this is one of the key reason why I use RHEL/CentOS rather
than Debian/Ubuntu.
> Backups primarily sits on completely different storage.
>
> If you keep backup of data in same pool:
>
> 1.)
> error on this in single chunk shared by all your backup + origin -
> means it's total data loss - especially in case where filesystem are
> using 'BTrees' and some 'root node' is lost - can easily render you
> origin + all backups completely useless.
>
> 2.)
> problems in thin-pool metadata can make all your origin+backups just
> an unordered mess of chunks.
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?
>
> 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?
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:[~2018-03-01 7:14 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 [this message]
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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