Lab 16.1 : logical volume based on 2 partitions of a single loop device is no mounted on boot

gsusmonzon

Hello,

 I completed the Lab 16.1 with a setup based on a loop device with 2 partitions. The volume group is created from /dev/loop1p1 /dev/loop1p2 and everything is working.

 However I dont know how to do it persists between boots.

 My guess is that fstab is trying to mount the logical volume but the 2 loop-partitions are not available. I suspect that losetup should be run at some point during boot before /etc/fstab enters into play.

 Could you help me (or point me in the right direction) to make the logical volume persists between boots. I know that this is not a typical setup, but I want to understand if this path is possible or not and what is the reason.

Thanks in advance

These are the commands I followed

#create loop device and partitions
dd if=/dev/zero of=/imagefile2 bs=1M count=1024
fdisk /imagefile2
...
       Device Boot      Start         End      Blocks   Id  System
/imagefile2p1            2048      514047      256000   8e  Linux LVM
/imagefile2p2          514048     1026047      256000   8e  Linux LVM

#setup loop device
losetup --show --partscan --find /imagefile2
> /dev/loop1

#Now create the physical volumes
pvcreate /dev/loop1p1
pvcreate /dev/loop1p2
pvdisplay

#create virtual groups
vgcreate myvg /dev/loop1p1 /dev/loop1p2
vgdisplay

#create logical volumes. Ex 300Mb
lvcreate -L 300M -n mylvm myvg
lvdisplay

#partition the logical volume
mkfs.ext4 /dev/myvg/mylvm

#mount
echo "/dev/myvg/mylvm /mnt/mylvm ext4 defaults 0 0" >> /etc/fstab
mkdir -p /mnt/mylvm
mount -a

luisviveropena

Hi,

You may try to add the loop device to /etc/fstab, and it should work after a restart. But I'm not sure if it's going to be ready to be part of a LVM group. But you can try

Regards,

Luis.

gsusmonzon

Thanks Luis. No luck.

I tried to mount the loop device in fstab but it failed. The problem is that the loop device has not filesystem itself, but it is made of 2 partitions of type 8e. So the following fails

/imagefile2    /mnt/tempdir2  ext4    loop,rw            1 2

/dev/myvg/mylvm /mnt/mylvm ext4 defaults 0 2

I guess that the solucion is in executing

losetup --show --partscan --find /imagefile2

during boot (and before /etc/fstab starts mounting the partitions or at least before the logical volume is mounted).

I dont know if it is possble, and I lack the knowledge of the booting process for doing this.

Another option would be mounting it via a systemd that executes the losetup, but it looks a bit hacky.

I think it is enough for an scenario that does not reflect a real use case. In a real world I would have 2 real disks.

Thanks

 

 

luisviveropena

Yeah, you may need to create a service, so you can get the device ready at the right time. If you have time you can play with it. If not, a better possibility is to resize the hard disk, so you can have enough space to create a couple of partitions.

Regards,

Luis.