Bug 242074

Summary:	device-mapper mirror: Writes to non-synced regions must be marked/cleared in the log
Product:	Red Hat Enterprise Linux 4	Reporter:	Jonathan Earl Brassow <jbrassow>
Component:	kernel	Assignee:	Jonathan Earl Brassow <jbrassow>
Status:	CLOSED ERRATA	QA Contact:	Martin Jenner <mjenner>
Severity:	low	Docs Contact:
Priority:	low
Version:	4.5	CC:	mbroz
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	RHBA-2007-0791	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2007-11-15 16:28:01 UTC	Type:	---
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:	242075, 243773

Description Jonathan Earl Brassow 2007-06-01 15:29:34 UTC

During normal mirror operation (i.e. when the devices are
in-sync), a write is preceded by marking the log and is
followed by clearing the log.  However, when the mirror is
in recovery, the marks and clears are not performed.

For single machine mirroring, this is fine; because the
mirroring code can control conflicts between writes and
re-syncing via the region hashing code.  However, this
is not possible in a cluster.  If a remote machine does not
mark the log for a non-sync'ed write, it is impossible
to tell when/if there will be a conflict with the re-syncing
process.  [RHEL 4 must currently delay writes to non-synced
regions until they have been recovered - a sometimes excessive
delay.]

Marking/clearing regions that are not-in-sync will allow
the (cluster) logging code to avoid handing out re-sync work
that might conflict with an outstanding write.  It can also
delay writes briefly to a region that is being resync'ed.

Comment 1 RHEL Program Management 2007-06-01 15:45:07 UTC

This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release.  Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products.  This request is not yet committed for inclusion in an Update
release.

Comment 2 Jonathan Earl Brassow 2007-06-01 18:32:34 UTC

assigned -> post

Comment 3 RHEL Program Management 2007-06-01 18:41:51 UTC

This request was evaluated by Red Hat Kernel Team for inclusion in a Red
Hat Enterprise Linux maintenance release, and has moved to bugzilla 
status POST.

Comment 4 Jason Baron 2007-06-29 22:20:03 UTC

committed in stream U6 build 55.15. A test kernel with this patch is available
from http://people.redhat.com/~jbaron/rhel4/

Comment 7 errata-xmlrpc 2007-11-15 16:28:01 UTC

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2007-0791.html