After I seen the talk about VDO:
  https://www.youtube.com/watch?v=7CGr5LEAfRY
I went ahead and tried it.
I tried it on small (12GB) sample of Copr data and I saved 20-30% data.
I then deployed it on production server retrace.fedoraproject.org and saved 
there 15% out of 2TB.

Several notes: The RPM packages are only available for RHEL. Recently the 
public github has been updated with version of
VDO, which should work on Fedora. No RPM available for Fedora yet though.

Here are my notes:

# vdo create --name=vdo1 --device=/dev/vdb --vdoLogicalSize=1T

# mkfs.ext4 /dev/mapper/vdo1
Some slides suggest to use -E discard. This is not needed for new volumes. See 
vdo-devel mailing list for reasoning.

# mount -o discard /dev/mapper/vdo1 /mnt/a


Probably best scenario is to create vdo on whole disk and then make PV from 
whole VDO disk and put LVM on top of that.

When you already have data, you cannot convert your disk to VDO. You need 
create new VDO disk, format it, mount it and
copy the data.
In my case, due limited space for migration I created a small LVM volume 
"vdosrv":

# lvcreate -L 80G -n vdosrv vol0

I converted it to VDO which claims to have 2TB of vitual total size

# vdo create --name=srv18 --device=/dev/vol0/vdosrv --vdoLogicalSize=2T

# mkfs.ext4 /dev/mapper/srv18

See how many space is *actually* free.
# vdostats

# mkdir /mnt/srv18
# mount -o discard /dev/mapper/srv18 /mnt/srv18

Now I moved some data from old volume to /mnt/srv18. I shrank the FS of old 
volume, I shrank the old LV. And then I
enlarged the new LV.

# lvresize -L +400G /dev/vol0/vdosrv

and let know vdo that it can use the new space:

# vdo growPhysical -n srv18

I repeated this several times.

I have to say that my experience is so far good.

I hope that my notes help someone.

Miroslav
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