Unable to mount lvmcache root device at boot time

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apport-collect 1423796

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

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

This is an lvm2 bug and I wanted to report it to lvm2, not Linux. I remember that I exactly typed lvm2, I don't know why it was still reported to linux. Could someone help me to sort it out?

Status changed to 'Confirmed' because the bug affects multiple users.

I also tried the instructions in
http://forums.debian.net/viewtopic.php?f=5&t=119644
but still cannot reboot into cached hdd system

removing the cache (lvremove lvcache) every time I fail to boot, by using a rescue usb, gave me some corruption and was just inconvenient to further experiment. so I ended up giving up until someone else succeeds using lvmcache.

My use would be a laptop with a small ssd 24GB drive and I think this would be a cool way to speed up the system. actually it was intended for that and the MS windows system did that before I wiped it out. Setting up the lvm and installing ubuntu was easy, setting up the lvmcache was easy too... but couldn't manage to make it boot :/

MegaBrutal, can you give some instructions. I followed the instructions at
 http://forums.debian.net/viewtopic.php?f=5&t=119644
but still couldn't boot

OK, I managed! I had to add more modules

sudo echo "dm_cache" >> /etc/initramfs-tools/modules
sudo echo "dm_cache_mq" >> /etc/initramfs-tools/modules
sudo echo "dm_persistent_data" >> /etc/initramfs-tools/modules
sudo echo "dm_bufio" >> /etc/initramfs-tools/modules

plus, add cache_check as in
 http://forums.debian.net/viewtopic.php?f=5&t=119644

Booted!

This is how I set up the lvmcache
sudo vgextend LinuxVG /dev/sdb2
sudo lvcreate -L 10G -n rootCacheLV LinuxVG /dev/sdb2
sudo lvcreate -L 24M -n rootCacheMetaLV LinuxVG /dev/sdb2
sudo lvcreate -L 10G -n homeCacheLV LinuxVG /dev/sdb2
sudo lvcreate -L 24M -n homeCacheMetaLV LinuxVG /dev/sdb2
sudo lvconvert --type cache-pool --poolmetadata LinuxVG/rootCacheMetaLV --cachemode writethrough LinuxVG/rootCacheLV
sudo lvconvert --type cache-pool --poolmetadata LinuxVG/homeCacheMetaLV --cachemode writethrough LinuxVG/homeCacheLV
sudo lvconvert --type cache --cachepool LinuxVG/rootCacheLV LinuxVG/rootLV
sudo lvconvert --type cache --cachepool LinuxVG/homeCacheLV LinuxVG/homeLV

where LinuxVG has the root at rootLV and home at homeLV and sdb2 is an SSD

Thank you George! Your contribution was the final thing I needed to get this to work :

http://askubuntu.com/questions/620480/how-to-install-ubuntu-with-both-disk-encryption-and-ssd-caching

I have the same problem with Ubuntu 15.04
The solution of gmoutso worked thanks !

Is this corrected in the 15.10 ?

I'm running Ubuntu 15.10 and I was unable to get gmoutso's solution working.

Correction, I was able to get gmoutso's solution to work. I realized that I needed to create a separate boot partition that didn't use lvm caching. In retrospect, this makes a lot of sense.

After making my system work again, which took a while since most live media and even the installer don't support LVM cache, I had it working for writeback on my system with the following.

/etc/initramfs-tools/hooks/lvm2_cache
{{{
#!/bin/sh

PREREQ="lvm2"

prereqs()
{
    echo "$PREREQ"
}

case $1 in
prereqs)
    prereqs
    exit 0
    ;;
esac

if [ ! -x /sbin/lvm ]; then
    exit 0
fi

. /usr/share/initramfs-tools/hook-functions

copy_exec /usr/sbin/cache_check
copy_exec /usr/sbin/cache_dump
copy_exec /usr/sbin/cache_metadata_size
copy_exec /usr/sbin/cache_repair
copy_exec /usr/sbin/cache_restore

for x in dm_cache_cleaner dm_cache_smq dm_cache dm_persistent_data dm_bio_prison
do
    manual_add_modules ${x}
done
}}}

That new file could be added to the thin-provisioning-tools which would trigger an initramfs update.

I forgot to remove cache_dump, cache_restore and cache_metadata_size which are not needed to boot.

@George:
George Moutsopoulos (gmoutso) wrote on 2015-04-29:
> OK, I managed! I had to add more modules
>
> sudo echo "dm_cache" >> /etc/initramfs-tools/modules
> sudo echo "dm_cache_mq" >> /etc/initramfs-tools/modules
> sudo echo "dm_persistent_data" >> /etc/initramfs-tools/modules
> sudo echo "dm_bufio" >> /etc/initramfs-tools/module
---
Not exactly related to the original bug, but wanted to address a boo-boo in the above.
sudo echo "string" won't use root's access/permissions to write to the files when using the shell-redirection operators '>' or '>>'. sudo will execute 'echo' with root privs, and that will echo "dm_cache" (et al.), however, that output is redirected by the *SHELL* (running as
"whoever is running the shell") -- usually the user.

To get around this problem (and not saying there might not be any easier ways, as this seemed a bit roundabout to get what I wanted (have root write the output to "wherever"), I used
"dd", as in:

echo "dm_cache"|sudo dd of=destination status=none

 or to append:

echo "dm_cache"|sudo dd status=none oflag=append conv=notrunc of=/etc/initramfs-tools/modules

 or to do all at once:

(echo dm_cache
echo dm_cache_mq
echo dm_persistent_data
echo dm_bufio)|sudo dd status=none oflag=append conv=notrunc of=/initramfs-tools/modules

I wanted to write a single "char" to a file in /proc/sys/vm (drop_caches).

Perhaps needless to say, I put it in a script file to save on typing. :-)

Same bug in 17.04: configure lvmcache and reboot - system can't map cached device to /dev/mapper/
Fixed by update initramfs with hook in upper comment: https://bugs.launchpad.net/ubuntu/+source/lvm2/+bug/1423796/comments/12

I just ran into this with a cleanly installed 17.04. Figured it out myself, added "copy_exec /usr/sbin/cache_check" to /usr/share/initramfs-tools/hooks/lvm2 in order to fix it.

Can we PLEASE get this bug -- which renders systems UNBOOTABLE after attaching a cache -- fixed, especially since there are good and reasonable patches available already (#12)?

Related to debian bug #773731

This is still broken in Ubuntu 18.04.

yah I have actually never seen a bug fixed on the Ubuntu bug tracker, just deal with it upstream or use a different distribution.
IMO Ubuntu should delete bugs.launchpad.net and just merge pull requests on github/etc.

Still a problem in 20.04...

I confirm, still there in 20.04