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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

I built Precise test kernel with a backport of commit 9dedf60 and a
cherry-pick of commit d1901ef.

The test kernel can be downloaded from:

http://kernel.ubuntu.com/~jsalisbury/lp1446786

Can folks affected by this bug test this kernel and see if it resolves
the bug?

Thanks in advance!

** Also affects: linux (Ubuntu Precise)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Precise)
       Status: New => In Progress

** Changed in: linux (Ubuntu Precise)
   Importance: Undecided => Medium

** Changed in: linux (Ubuntu Precise)
     Assignee: (unassigned) => Joseph Salisbury (jsalisbury)

** Changed in: linux (Ubuntu)
       Status: Triaged => In Progress

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Joseph Salisbury (jsalisbury)

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https://bugs.launchpad.net/bugs/1446786

Title:
  Wrong read balance when a drive is write-mostly

Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Precise:
  In Progress

Bug description:
  This bug related to `mdadm` `--write-mostly` option. When we create
  SSD for read operation, but want to use HDD to mirror SSD content we
  can create RAID-1 with SSD and 'write-mostly' HDD disk.

  In Ubuntu kernel there is a bug, which lead to havy read from both SSD
  and HDD drives. More over if we add HDD as regular disk and SSD as a
  'write-mostly' replica most read operations will go to SSD drive
  (which is clear from sources and we have prove it in our setup).

  In upstream kernel sources this was already fixed:

  https://github.com/torvalds/linux/commit/63a7d0a9160421a23baac407847e484e8488d12a

  Could you backport this functionality? - This patch looks safe to
  apply as is.

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