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Re: [linux-lvm] lvcreate --thin gives "unknown segment type" error



Dne 22.7.2013 13:23, Kumar amit mehta napsal(a):
On Mon, Jul 22, 2013 at 06:57:42AM -0400, Kumar amit mehta wrote:
On Mon, Jul 22, 2013 at 02:15:36PM +0200, Zdenek Kabelac wrote:
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.


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).


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.


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