Bug 1903612

Summary:	RBD fast-diff regression introduced due to snapshot-based mirroring changes
Product:	[Red Hat Storage] Red Hat Ceph Storage	Reporter:	Jason Dillaman <jdillama>
Component:	RBD	Assignee:	Jason Dillaman <jdillama>
Status:	CLOSED ERRATA	QA Contact:	Harish Munjulur <hmunjulu>
Severity:	high	Docs Contact:
Priority:	unspecified
Version:	4.2	CC:	asakthiv, ceph-eng-bugs, gmeno, hmunjulu, kdreyer, vereddy
Target Milestone:	---	Keywords:	Regression
Target Release:	4.2
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	ceph-14.2.11-94.el8cp, ceph-14.2.11-94.el7cp	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-01-12 14:58:46 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:

Description Jason Dillaman 2020-12-02 13:59:57 UTC

Description of problem:
A regression was introduced during the introduction of snapshot-based mirroring that results in the fast-diff feature being broken. 

"rbd du" will not only take orders of magnitude longer, it will also potentially return incorrect results if the fast-diff feature is not enabled but object-map is enabled.

"rbd-mirror" in snapshot-based mirroring mode will not be able to use the speed optimization of only testing dirty blocks and instead will query deltas for each data block from remote OSDs. If the fast-diff feature is not enabled and object-map is enabled, it will result in data corruption.

Version-Release number of selected component (if applicable):
4.2

How reproducible:
100%

Steps to Reproduce:
1. create a large image
2. 'rbd du' against the image

Actual results:
Results can take minutes for large enough images.

Expected results:
Should execute almost immediately because fast-diff will be used


Additional info:

Comment 1 Jason Dillaman 2020-12-02 14:12:24 UTC

Note: this might also effect the dashboard since it calculates RBD image disk usage in the background if fast-diff feature is enabled, but the librbd API is not correctly using fast-diff.

Comment 5 Veera Raghava Reddy 2020-12-15 17:26:14 UTC

Hi Jason, From the description the bZ seems to be a regression and don't have workaround. We should include this BZ into 4.2

Comment 7 Veera Raghava Reddy 2020-12-15 18:18:16 UTC

Hi Jason, Thanks for sharing the details. Proposing the BZ for 4.2 based on the potential impact to OSP customers.

Comment 15 Harish Munjulur 2020-12-23 21:32:27 UTC

Verified on ceph version 14.2.11-95.el8cp

Comment 17 errata-xmlrpc 2021-01-12 14:58:46 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 (Important: Red Hat Ceph Storage 4.2 Security and Bug Fix update), 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://access.redhat.com/errata/RHSA-2021:0081