Wrong read balance when a drive is write-mostly

[Dmitry Maslennikov]

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.

[Dmitry Maslennikov (maslennikovdm)]

Forget to add that we use Ubuntu 12.04

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1446786

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Joseph Salisbury (jsalisbury)]

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!

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu Precise) because there has been no activity for 60 days.]

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]