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Bug 1166873 - LVM Thin: Ability to resize thinsnaps to something other than their origin
Summary: LVM Thin: Ability to resize thinsnaps to something other than their origin
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: lvm2
Version: 7.1
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Zdenek Kabelac
QA Contact: cluster-qe@redhat.com
URL:
Whiteboard:
Depends On:
Blocks: 1119323
TreeView+ depends on / blocked
 
Reported: 2014-11-21 20:06 UTC by Jonathan Earl Brassow
Modified: 2021-09-03 12:52 UTC (History)
10 users (show)

Fixed In Version: lvm2-2.02.125-1.el7
Doc Type: Enhancement
Doc Text:
lvm2 has extend support for thin snapshot of external origins. Thin volumes now can be resized to any size.
Clone Of:
Environment:
Last Closed: 2015-11-19 12:45:52 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Bugzilla 1143823 1 None None None 2021-01-20 06:05:38 UTC
Red Hat Product Errata RHBA-2015:2147 0 normal SHIPPED_LIVE lvm2 bug fix and enhancement update 2015-11-19 11:11:07 UTC

Internal Links: 1143823

Description Jonathan Earl Brassow 2014-11-21 20:06:13 UTC 
Add the ability to resize thinSnaps to something other than their origin's size.  If grown, it should be possible to have the extension return zeros.
Comment 1 Zdenek Kabelac 2014-12-05 15:18:11 UTC 
This BZ has unclear description.

Thin snapshots are instantly created as 'unique' thin volumes - so basically once user make a snapshot - thin volume could be then independently resized.

The read content of new size is basically based on 'thin-pool' zeroing feature state.

You always read zeros from 'unprovisioned' chunks.

And you read either zeros from zeroed thin pool of 'chunk-garbage' from unzeroed thin-pool - depending on amount of written size on chunk provisioning.

Unlike with old 'snapshots' there is no limitation what user could do with thin snapshot.
Comment 2 Samuel Bronson 2015-02-27 18:21:47 UTC 
(In reply to Zdenek Kabelac from comment #1)
> This BZ has unclear description.
> 
> Thin snapshots are instantly created as 'unique' thin volumes - so basically
> once user make a snapshot - thin volume could be then independently resized.

I suspect this is about resizing thin volumes that have external origins.

> The read content of new size is basically based on 'thin-pool' zeroing
> feature state.
> 
> You always read zeros from 'unprovisioned' chunks.

My understanding is that this was not the case with external origins until https://github.com/torvalds/linux/commit/e5aea7b49f2b1fd01f35ca7abeb76f5c56128a55

To actually make use of this change, someone would have to update the entry for the "external_origin_suspend" feature in lvm2/lib/thin/thin.c; right now it has a bogusly-high placeholder version number "9, 11", which should presumably be replaced with the "1, 13" from the kernel commit above.

(And lets not forget the case of extending thin volumes that had been shrunk to below the size of their external origins; iirc there's a comment about that somewhere in the lvm2 code ...)
Comment 6 Zdenek Kabelac 2015-06-19 19:12:44 UTC 
Started to improve usage of thin volumes with external origin that are unaligned with thin-pool chunk size with this upstream patch series:

https://www.redhat.com/archives/lvm-devel/2015-June/msg00055.html

With this patch set user can take thin-snapshot of external origin volume size unrelated to thin-pool chunk size.

Such thin volume could be resized to any size.
Comment 9 errata-xmlrpc 2015-11-19 12:45:52 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2147.html
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