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Bug 1242239 - md raid1 writemostly feature broken
md raid1 writemostly feature broken
Status: CLOSED ERRATA
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: kernel (Show other bugs)
6.6
Unspecified Unspecified
unspecified Severity high
: rc
: ---
Assigned To: Jes Sorensen
Zhang Yi
:
Depends On:
Blocks: 1270066
  Show dependency tree / graph
 
Reported: 2015-07-12 09:25 EDT by Dwight (Bud) Brown
Modified: 2016-05-10 18:51 EDT (History)
5 users (show)

See Also:
Fixed In Version: kernel-2.6.32-584.el6
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Environment:
Last Closed: 2016-05-10 18:51:23 EDT
Type: Bug
Regression: ---
Mount Type: ---
Documentation: ---
CRM:
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2016:0855 normal SHIPPED_LIVE Moderate: kernel security, bug fix, and enhancement update 2016-05-10 18:43:57 EDT

  None (edit)
Description Dwight (Bud) Brown 2015-07-12 09:25:00 EDT 
Description of problem:

Customer encountered mdraid broken writemostly feature - both disks in mirror are read from fairly equally even with writemostly set on just one leg.

writemostly feature broken by upsteam commit:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/md/raid1.c?id=9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc

fixed by upstream commit:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/md?id=d1901ef099c38afd11add4cfb3312c02ef21ec4a

"
md/raid1: fix read balance when a drive is write-mostly.
When a drive is marked write-mostly it should only be the
target of reads if there is no other option.

This behaviour was broken by

commit 9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc
    md/raid1: read balance chooses idlest disk for SSD

which causes a write-mostly device to be *preferred* is some cases.
"




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


How reproducible:
100%

Steps to Reproduce:
1. create mirror
2. set writeonly on one leg
3. perform reads.

Actual results:
reads from both legs of mirror

Expected results:
reads avoided on leg of mirror marked writeonly

Additional info:
Comment 5 Aristeu Rozanski 2015-11-04 15:44:21 EST 
Patch(es) available on kernel-2.6.32-584.el6
Comment 8 Zhang Yi 2016-01-28 08:59:48 EST 
Verified on kernel-2.6.32-584.el6:
I used two disks: sdb/sdc for test, after set one disk: sdc with writemostly, the MB_read of iostat for sdc becomes 0.

The patch from commet 6 also exist on 2.6.32-584.el6.

Change to verified.
Comment 10 errata-xmlrpc 2016-05-10 18:51:23 EDT 
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/RHSA-2016-0855.html
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