Bug 761580

Summary:	Backport dm-queue-length and dm-service-time path selectors from 2.6.34.
Product:	Red Hat Enterprise Linux 6	Reporter:	Don Hoover <donhoover>
Component:	kernel	Assignee:	LVM and device-mapper development team <lvm-team>
Status:	CLOSED NOTABUG	QA Contact:	Storage QE <storage-qe>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	6.4	CC:	agk, bmarzins, dwysocha, heinzm, mbroz, msnitzer, prajnoha, prockai, zkabelac
Target Milestone:	rc
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-12-08 17:05:57 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:

Description Don Hoover 2011-12-08 16:22:18 UTC

Description of problem:
Any chance of back porting the dm-service-time and dm-queue-length path selectors from dm-multipath that were included in 2.6.34 into the RHEL6 kernel for RHEL 6.4+?

These new algorythims pretty much bring dm-multipath into 100% capable of any alleged feature benefits over commercial products such as EMC PowerPath.

Having more than just simple round-robin is pretty much the only features missing from dm-multipath in comparison to those commercial products, so we are anxious to get these features in our RHEL systems native capabilites.

Comment 2 Mike Snitzer 2011-12-08 17:05:57 UTC

RHEL6 has always had these new path selectors.  Closing NOTABUG.

Comment 3 Mike Snitzer 2011-12-08 17:12:27 UTC

FYI, the path-selector that is used can be configured in /etc/multipath.conf

Either in the 'defaults' section (applies to all mpath devices), e.g.:

defaults
{
        ...
        selector                "queue-length 0"
}                                                                                                                                                                      

or in the per mpath 'device' section, e.g.:

devices
{
        device
        {
                ...
                path_selector   "service-time 0"
        }                                                                                                                                                              
}                                                                                                                                                                      

Not specifying a selector defaults to "round-robin 0"


Other RHEL6 multipath info is available here:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/DM_Multipath/MPIO_Overview.html
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/DM_Multipath/config_file_devices.html

Comment 4 Don Hoover 2011-12-08 19:14:12 UTC

Thanks so much for the detailed answer.  It is much appreciated.