Re: Why does Anaconda leave 100GB empty for LVM Thin ?

[David Lehman <dlehman@xxxxxxxxxx>]

Hi,

On Fri, Aug 27, 2021 at 3:00 PM Sreyan Chakravarty <sreyan32@xxxxxxxxx> wrote:

Hi,

I have just installed a new Fedora 33 KDE system. 

So this is my layout:

NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                                             8:0    0 931.5G  0 disk   
├─sda1                                          8:1    0   512M  0 part  /boot/efi
├─sda2                                          8:2    0     1G  0 part  /boot
└─sda3                                          8:3    0   930G  0 part   
 └─luks-aee439f3-528c-4481-ab09-622304e727bc 253:0    0   930G  0 crypt  
   ├─vgfedora-pool00_tmeta                   253:1    0   424M  0 lvm    
   │ └─vgfedora-pool00-tpool                 253:3    0 829.2G  0 lvm    
   │   ├─vgfedora-fedora                     253:4    0 829.2G  0 lvm   /
   │   └─vgfedora-pool00                     253:5    0 829.2G  1 lvm    
   └─vgfedora-pool00_tdata                   253:2    0 829.2G  0 lvm    
     └─vgfedora-pool00-tpool                 253:3    0 829.2G  0 lvm    
       ├─vgfedora-fedora                     253:4    0 829.2G  0 lvm   /
       └─vgfedora-pool00                     253:5    0 829.2G  1 lvm   

The same thing as above in pastebin: https://pastebin.com/raw/xwXngMRh

If you notice that /dev/sda3 is of size 930G, but the volume group is only 829.2 G.

Why is that ? I have selected the size of the volume group as "Large as possible", but still 100G is left out.

Is this some kind of recommended setting for thin-LVMs ?

I am selecting Thin-LVM with LUKS2 during the install.

Can someone help me understand why this is happening and how I can fix it ? 

There are some circumstances under which LVM may need additional space for thin pool metadata. When we added support for thin provisioning they strongly recommended that we reserve a portion of the volume group space for this purpose.Initially it was 20% of the pool size, but the calculation may be more nuanced now. I wouldn't consider removing this bit of free space "fixing" anything unless you plan to actively monitor your system to ensure that your thin pool doesn't run out of space for metadata.

 

Will making a custom kickstart help here ?

Maybe... It has been a while since I worked on this code, but you _might_ be able to override this in kickstart using `--reserved-space` or `--reserved-percent` options to the `volgroup` command.

HTH,

David

 

--

Regards,

Sreyan Chakravarty

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