lvcreate --thin gives "unknown segment type" error

configure --with-thin=internal

(and you will likely miss '--enable-udev_sync'

Quoted 3 lines · Zdenek Kabelac

configure --with-thin=internal

(and you will likely miss '--enable-udev_sync'

Thank you, it worked!

However, It seems that "discards" behavior for thin pool is not supported on RHEL 6.4. Please confirm.

# ./configure --with-thin=internal --enable-debug

# make; make install

# lvcreate --discards passdown -L 1G -T thinvg1/thinlv1
  Logical volume "thinlv1" created

# lvs -o +devices|grep -i thinlv1
  thinlv1       thinvg1       twi-a-tz-   1.00g               0.00
thinlv1_tdata(0)

# dmesg
device-mapper: thin: Data device (dm-3) discard unsupported: Disabling
discard passdown.

<snip>
if (reason) {
DMWARN("Data device (%s) %s: Disabling discard

passdown.", bdevname(data_bdev, buf), reason);
                pt->adjusted_pf.discard_passdown = false;
        } 

<snip>

Seems that we'll reach here if QUEUE_FLAG_DISCARD flag in the request queue is not set.

Hi,

While trying to create thin provisioned volume, I'm getting "unknown segment type" error. Please see the logs below:

# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 6.4 (Santiago)

# uname -r
2.6.32-358.el6.x86_64

# dmsetup targets
thin-pool        v1.5.1
thin             v1.5.1
multipath        v1.5.0
mirror           v1.12.0
striped          v1.5.6
linear           v1.1.0
error            v1.0.1

# lvm version
   LVM version:     2.02.99(2)-git (2012-10-22)
   Library version: 1.02.78-git (2012-10-22)
   Driver version:  4.23.6

# vgs|grep -i testvg
testvg 2 0 0 wz--n- 3.99g 3.99g

# pvs -o +devices|grep -i testvg
   /dev/vdc   testvg        lvm2 a--  2.00g    2.00g
   /dev/vde   testvg        lvm2 a--  2.00g    2.00g

# lvcreate -L 1G -T testvg/thinlv1 -vvvv
#libdm-config.c:908       Setting activation/monitoring to 1
#lvmcmdline.c:1102         Processing: lvcreate -L 1G -T testvg/thinlv1 -vvvv
#lvmcmdline.c:1105         O_DIRECT will be used
#libdm-config.c:844       Setting global/locking_type to 1
#libdm-config.c:908       Setting global/wait_for_locks to 1
#locking/locking.c:241       File-based locking selected.
#libdm-config.c:813       Setting global/locking_dir to /var/lock/lvm
#libdm-config.c:908       Setting global/prioritise_write_locks to 1
#unknown/unknown.c:102       Initialised segtype: thin
   WARNING: Unrecognised segment type thin
#lvcreate.c:746   Unable to create LV with unknown segment type thin. <-
   Run `lvcreate --help' for more informationat am I missing?

What am I missing?

Quoted 15 lines · Zdenek Kabelac

Quoted 3 lines

configure --with-thin=internal

(and you will likely miss '--enable-udev_sync'

Thank you, it worked!

However, It seems that "discards" behavior for thin pool is not supported on RHEL 6.4. Please confirm.

# ./configure --with-thin=internal --enable-debug

# make; make install

# lvcreate --discards passdown -L 1G -T thinvg1/thinlv1
   Logical volume "thinlv1" created

Quoted 8 lines

# lvs -o +devices|grep -i thinlv1
   thinlv1       thinvg1       twi-a-tz-   1.00g               0.00
thinlv1_tdata(0)

# dmesg
device-mapper: thin: Data device (dm-3) discard unsupported: Disabling
discard passdown.

I'm invoking these commands on a VM. I do not know, from where these storage were mapped to my VM(were done my some storage admin). However

It's your backend device used for thinpool data which doesn't support discard. So it fallbacks to nopassdown behaviour (discard is processed only at pool level).

Quoted 3 lines

I'm invoking these commands on a VM. I do not know, from where these storage were mapped to my VM(were done my some storage admin). However

Important piece of puzzle - if you want to see TRIM command hits your storage, your storage needs to support it ;)

BTW it's perfectly ok to use thin pool only with nopassdown.

Zdenek

NOTE: issue_discard in lvm.conf is not related in any way with --discards option for thin pool creation.