Comment 13 for bug 1896578

Hi everyone,

The original patch author, Xiao Ni, has sent a V2 patchset to the linux-raid mailing list for feedback. This new patchset fixes the problems the previous version had, namely, properly calculating the discard offset for second and onward disks, and correctly calculates the stripe size in far layouts.

The patches are:

https://www.spinics.net/lists/raid/msg67208.html
https://www.spinics.net/lists/raid/msg67212.html
https://www.spinics.net/lists/raid/msg67213.html
https://www.spinics.net/lists/raid/msg67209.html
https://www.spinics.net/lists/raid/msg67210.html
https://www.spinics.net/lists/raid/msg67211.html

We now need to thoroughly test and provide feedback to Xiao and the Raid subsystem maintainer before these patches can get merged into mainline again. We really need to make sure that these patches don't cause any data corruption.

I have backported the patchset to the 4.15, 5.4 and 5.8 kernels.

Backports for 5.4 and 5.8 kernels:

https://paste.ubuntu.com/p/vPFFPMjhbv/
https://paste.ubuntu.com/p/MCGH8v7Rqk/
https://paste.ubuntu.com/p/rppy39Qgkz/
https://paste.ubuntu.com/p/Dsqy4PQNzJ/
https://paste.ubuntu.com/p/mZ9VDBD8d5/
https://paste.ubuntu.com/p/vJNYZyGTWH/
https://paste.ubuntu.com/p/M4sMwhgWTj/

Backports for the 4.15 kernel:

https://paste.ubuntu.com/p/X9rRHT59qf/
https://paste.ubuntu.com/p/VWwW9JbBHy/
https://paste.ubuntu.com/p/pFY3YbBW6t/
https://paste.ubuntu.com/p/JKg4KcHwPB/
https://paste.ubuntu.com/p/C4sf2r9jS4/

I have built test kernels for bionic, bionic HWE, focal and groovy.

Performance testing confirms that the testcase for formatting a Raid10 array on NVMe disks drops from 8.5 minutes to about 6 seconds, on AWS i3.8xlarge, due to the speedup in block discard.

https://paste.ubuntu.com/p/NNGqP3xdsc/

I have also run through the data corruption regression reproducer from bug 1907262, and throughout the process, the /sys/block/md0/md/mismatch_cnt was always 0, and all deep fsck checks came back clean for individual disks.

https://paste.ubuntu.com/p/5DK57TzdFH/

I am happy with these results, and its time to get some wider testing on these patches.

If you are interested in helping to test, please use dedicated test servers, and not production systems. These patches have caused data corruption before, so only place data on the Raid10 array that you have copies of elsewhere, and assume that total data loss could happen anytime.

Please note, these test kernels are NOT SUPPORTED by Canonical, and are for TEST PURPOSES ONLY. ONLY install in a dedicated test environment.

Instructions to Install (on a Bionic or Focal or Groovy system):
1) sudo add-apt-repository ppa:mruffell/lp1896578-test
2) sudo apt update

For Bionic:
3) sudo apt install linux-image-unsigned-4.15.0-136-generic linux-modules-4.15.0-136-generic linux-modules-extra-4.15.0-136-generic linux-headers-4.15.0-136-generic

For Bionic HWE 5.4 or Focal:
3) sudo apt install linux-image-unsigned-5.4.0-66-generic linux-modules-5.4.0-66-generic linux-modules-extra-5.4.0-66-generic linux-headers-5.4.0-66-generic

For Groovy:
3) sudo apt install linux-image-unsigned-5.8.0-44-generic linux-modules-5.8.0-44-generic linux-modules-extra-5.8.0-44-generic linux-headers-5.8.0-44-generic

4) sudo reboot
5) uname -rv

Bionic:
4.15.0-136-generic #140+TEST1896578v20210212b1-Ubuntu SMP Fri Feb 12 03:00:17 UTC 2
Bionic HWE:
5.4.0-66-generic #74~18.04.2+TEST1896578v20210212b1-Ubuntu SMP Fri Feb 12 02:55:4
Focal:
5.4.0-66-generic #74+TEST1896578v20210212b1-Ubuntu SMP Fri Feb 12 06:30:51 UTC 20
Groovy:
5.8.0-44-generic #50+TEST1896578v20210212b1-Ubuntu SMP Fri Feb 12 06:19:49 UTC 20

Make sure the uname matches one of the above strings before you start testing and formatting Raid10 arrays.

We want to test formatting the arrays with xfs, ext4, and general usage over time with regular consistency checks and fstrims. We want to make sure that mismatch counts are 0, and all fsck -f runs are clean, and no data corruption happens.

If you have any problems whatsoever, please let me know.

Thanks,
Matthew