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Bug 1109974

Summary: need a more graceful error when attempting to cache an origin that is already cached
Product: Red Hat Enterprise Linux 7 Reporter: Corey Marthaler <cmarthal>
Component: lvm2Assignee: Zdenek Kabelac <zkabelac>
lvm2 sub component: Cache Logical Volumes QA Contact: Cluster QE <mspqa-list>
Status: CLOSED ERRATA Docs Contact:
Severity: medium    
Priority: unspecified CC: agk, heinzm, jbrassow, msnitzer, prajnoha, zkabelac
Version: 7.0   
Target Milestone: rc   
Target Release: ---   
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: lvm2-2.02.112-1.el7 Doc Type: Bug Fix
Doc Text:
Lvm2 supports caching only certain LV types. Missed check allowed to pass unsupported volume type into internal code which then thrown internal error message. Check for supported types is now correctly checked at command level.
 Story Points: ---
Clone Of:
: 1114078 (view as bug list) Environment:
Last Closed: 2015-03-05 13:09:01 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1114078, 1119326    

Description Corey Marthaler 2014-06-16 19:09:43 UTC 
Description of problem:
Attempt to cache an origin volume that has already been cached

Create origin (slow) volume
lvcreate -L 4G -n already_cached cache_sanity /dev/sde1

Create first cache data and cache metadata (fast) volumes
lvcreate -L 2G -n pool_1 cache_sanity /dev/sdc1
lvcreate -L 8M -n pool_1_meta cache_sanity /dev/sdc1
Create cache pool volume by combining the cache data and cache metadata (fast) volumes
lvconvert --type cache-pool --cachemode writethrough --poolmetadata cache_sanity/pool_1_meta cache_sanity/pool_1

Create cached volume by combining the cache pool (fast) and origin (slow) volumes
lvconvert --type cache --cachepool cache_sanity/pool_1 cache_sanity/already_cached

Create second cached volume by combining the cache pool (fast) and origin (slow) volumes
lvcreate -L 2G -n pool_2 cache_sanity /dev/sdc1
lvcreate -L 8M -n pool_2_meta cache_sanity /dev/sdc1
Create cache pool volume by combining the cache data and cache metadata (fast) volumes
lvconvert --type cache-pool --cachemode writethrough --poolmetadata cache_sanity/pool_2_meta cache_sanity/pool_2


Attempt to create another cached volume by combining the second cache pool (fast) and the already cached origin (slow) volume.

[root@host-001 ~]# lvs -a -o +devices
  LV                     Attr       LSize   Pool   Origin                  Devices                
  already_cached         Cwi-a-C---   4.00g pool_1 [already_cached_corig]  already_cached_corig(0)
  [already_cached_corig] -wi-ao----   4.00g                                /dev/sde1(0)
  [lvol0_pmspare]        ewi-------   8.00m                                /dev/sdf1(0)
  pool_1                 Cwi-a-C---   2.00g                                pool_1_cdata(0)
  [pool_1_cdata]         Cwi-aoC---   2.00g                                /dev/sdc1(0)
  [pool_1_cmeta]         ewi-aoC---   8.00m                                /dev/sdc1(512)
  pool_2                 Cwi-a-C---   2.00g                                pool_2_cdata(0)
  [pool_2_cdata]         Cwi-a-C---   2.00g                                /dev/sdc1(514)
  [pool_2_cmeta]         ewi-a-C---   8.00m                                /dev/sdc1(1026)

[root@host-001 ~]# lvconvert --type cache --cachepool cache_sanity/pool_2 cache_sanity/already_cached
  Internal error: The origin, already_cached, cannot be of cache type




Version-Release number of selected component (if applicable):
3.10.0-123.el7.x86_64
lvm2-2.02.105-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
lvm2-libs-2.02.105-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
lvm2-cluster-2.02.105-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
device-mapper-1.02.84-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
device-mapper-libs-1.02.84-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
device-mapper-event-1.02.84-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
device-mapper-event-libs-1.02.84-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
device-mapper-persistent-data-0.3.2-1.el7    BUILT: Thu Apr  3 09:58:51 CDT 2014
cmirror-2.02.105-14.el7    BUILT: Wed Mar 26 08:29:41 CDT 2014
Comment 2 Jonathan Earl Brassow 2014-07-23 03:18:06 UTC 
this should actually be allowed to stack cache on cache... see bug 727072.  It would be two layers of cache in that case.  Although, we may not have to do this in 7.1.
Comment 3 Zdenek Kabelac 2014-11-05 14:40:13 UTC 
https://www.redhat.com/archives/lvm-devel/2014-November/msg00040.html

As of now - disabled explicitly by lvm2 code.

We do not support snapshotting of cached volumes until we resolve what this actually means -  libdm currently requires snapshot to be a top-level LV so it's not going to work well in some orders.
Comment 5 Corey Marthaler 2014-11-20 20:48:16 UTC 
Verified the "Internal error" no longer shows up. However I'd argue the new warning message is actually more confusing than what the old internal error warning said, "The origin, $origin, cannot be of cache type"

[root@host-115 ~]# lvs -a -o +devices
 LV                     Attr       LSize Pool     Origin                 Data%  Meta%  Cpy%Sync Devices
 already_cached         Cwi-a-C--- 4.00g [pool_1] [already_cached_corig] 0.02   3.47   0.00     already_cached_corig(0)
 [already_cached_corig] owi-aoC--- 4.00g                                                        /dev/sdb1(0)
 [lvol0_pmspare]        ewi------- 8.00m                                                        /dev/sda1(0)
 [pool_1]               Cwi---C--- 2.00g                                 0.02   3.47   0.00     pool_1_cdata(0)
 [pool_1_cdata]         Cwi-ao---- 2.00g                                                        /dev/sdd1(0)
 [pool_1_cmeta]         ewi-ao---- 8.00m                                                        /dev/sdd1(512)
 pool_2                 Cwi---C--- 2.00g                                                        pool_2_cdata(0)
 [pool_2_cdata]         Cwi------- 2.00g                                                        /dev/sdd1(514)
 [pool_2_cmeta]         ewi------- 8.00m                                                        /dev/sdd1(1026)

[root@host-115 ~]# lvconvert --yes --type cache --cachepool cache_sanity/pool_2 cache_sanity/already_cached
  Cache is not supported with cache segment type of the original logical volume cache_sanity/already_cached.
Comment 7 errata-xmlrpc 2015-03-05 13:09:01 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-2015-0513.html