On 30/09/2020 10:00, David Madore wrote:
On Wed, Sep 30, 2020 at 05:03:28AM +0100, Wols Lists wrote:
uname -a ???
Linux vega.stars 4.9.237-vega #1 SMP Tue Sep 29 23:52:36 CEST 2020 x86_64 GNU/Linux
This is a stock 4.9.237 kernel that I compiled with gcc version 4.8.4
(Debian 4.8.4-1). RAID-related options in the config are:
CONFIG_MD=y
CONFIG_BLK_DEV_MD=y
CONFIG_MD_AUTODETECT=y
CONFIG_MD_LINEAR=m
CONFIG_MD_RAID0=y
CONFIG_MD_RAID1=y
CONFIG_MD_RAID10=m
CONFIG_MD_RAID456=m
CONFIG_MD_MULTIPATH=m
CONFIG_MD_FAULTY=m
# CONFIG_MD_CLUSTER is not set
CONFIG_ASYNC_RAID6_RECOV=m
CONFIG_RAID6_PQ=m
(I can, of course, put the full config somewhere).
mdadm --version ???
mdadm - v3.4 - 28th January 2016
(This is the version from Debian 9.13 "stretch" (aka oldstable).)
https://raid.wiki.kernel.org/index.php/Linux_Raid#When_Things_Go_Wrogn
So my guess was spot on :-)
You'll guess that this is a common problem, with a well-known solution...
https://raid.wiki.kernel.org/index.php/Easy_Fixes#Debian_9_and_Ubuntu
I should have clarified that I suffered no data loss. Since the
attempt to reshape simply does nothing (and the underlying filesystem
was read-only just in case), I was able to simply recreate the RAID5
array with --assume-clean. But I'd really like to convert to RAID6.
I can, of course, provide detailed information on the disks, but since
I can reproduce the problem on loopback devices, I imagine this isn't
too relevant.
I'm guessing you're on an older version of Ubuntu / Debian ?
Yes, Debian 9.13 "stretch" (aka oldstable).
That web page tells you, but basically it's what I call the
"frankenkernel problem" - the kernel has been updated to buggery, mdadm
is out-of-date, and they are not regression-tested. The reshape gets
stuck trying to start.
So the fix is to use an up-to-date rescue disk with matched kernel and
mdadm to do the reshape.
Oh - and once you're all back up and running, I'd build the latest mdadm
and upgrade to that. And don't try to reshape the array again, unless
you've upgraded your distro to something recent :-)
Cheers,
Wol
