Bug 1554241

Summary:	Problem attaching lvmcache to thinpool
Product:	[Red Hat Storage] Red Hat Gluster Storage	Reporter:	SATHEESARAN <sasundar>
Component:	rhhi	Assignee:	Gobinda Das <godas>
Status:	CLOSED DEFERRED	QA Contact:	SATHEESARAN <sasundar>
Severity:	high	Docs Contact:
Priority:	medium
Version:	rhhiv-1.5	CC:	godas, rhs-bugs, sabose, sasundar
Target Milestone:	---	Keywords:	Tracking
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Known Issue
Doc Text:	When bricks are configured asymmetrically, and a logical cache volume is configured, the cache volume is attached to only one brick. This is because the current implementation of asymmetric brick configuration creates a separate volume group and thin pool for each device, so asymmetric brick configurations would require a cache volume per device. However, this would use a large number of cache devices, and is not currently possible to configure using Cockpit. To work around this issue, first remove any cache volumes that have been applied to an asymmetric brick set. # lvconvert --uncache volume_group/logical_cache_volume Then, follow the instructions in https://access.redhat.com/documentation/en-us/red_hat_hyperconverged_infrastructure_for_virtualization/2.0/html-single/maintaining_red_hat_hyperconverged_infrastructure_for_virtualization/#config-lvmcache to create a logical cache volume manually.	Story Points:	---
Clone Of:
Clones:	1554242 (view as bug list)		Environment:
Last Closed:	2019-05-07 14:36:16 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:	1554242
Bug Blocks:

Description SATHEESARAN 2018-03-12 08:40:05 UTC

Description of problem:
-----------------------
With the current implementation ( with asymmetric brick configuration ), there could separate thinpools for each device. But lvmcache could be attached to only one thinpool. Need to have a clarity on this. 

Version-Release number of selected component (if applicable):
-------------------------------------------------------------
ovirt-cockpit-dashboard-0.11.14

How reproducible:
-----------------
Always

Steps to Reproduce:
-------------------
1. Start RHHI installation via cockpit
2. For 'host1', select 'sdb' for vmstore volume brick and select 'sdc' for data volume brick
3. Enable lvmcache

Actual results:
---------------
lvmcache is attached to one of the thinpool on one of the device 

Expected results:
-----------------
All the bricks ( XFS filesystems ) should able to make use of lvmcache 

Additional info:
----------------
There are 2 options possible. 
1. SSD could be partitioned and could act as lvmcache for each of the thinpool or 
2. one thinpool needs to be created out of multiple devices. 

But the latter approach is against the perf recommendation for RHGS, where 1 Disk -> 1 PV -> 1 VG -> 1 thinpool -> lv is preferred

Comment 1 Sahina Bose 2018-07-06 13:23:55 UTC

This needs to be retargeted. Sas, can we move it out of in-flight tracker

Comment 2 SATHEESARAN 2018-07-11 10:36:11 UTC

(In reply to Sahina Bose from comment #1)
> This needs to be retargeted. Sas, can we move it out of in-flight tracker

Sahina,

This will be a problem, when user tries to create bricks from separate devices and wanted to attach LVM cache to all thinpools or specific thinpool

We should document this behavior as the known_issue with the workaround

Comment 3 Sahina Bose 2018-07-16 04:45:04 UTC

Please provide doc_text for known issue

Comment 5 Gobinda Das 2018-07-24 06:30:08 UTC

Looks good to me.

Comment 6 Sahina Bose 2019-05-07 14:36:16 UTC

lvmcache is not high priority as there's no consistent performance improvement seen. Deferring this for now