On Fri, Jan 18, 2019 at 10:43:54AM +0200, Shaun Glass wrote: > # pvcreate /dev/sdf > # pvcreate /dev/sdg > # fdisk /dev/sdf (Created a partition with type fd) > # fdisk /dev/sdg (Created a partition with type fd) Storage works in layers, and each layer can only be one thing. So /dev/sdf can be either a PV, or a partition table, not both. It's convention to make it a partition table and leaving it out may cause you grief further down the road, when another software sees no partition table and helpfully creates one. The partition table gives you a new layer (/dev/sdf1) you can use for something else. If you put mdadm on /dev/sdf1 it gives you a new layer (/dev/md1) you can use for something else. If you put LVM on /dev/md1 it gives you a new layer (/dev/vg/lv) you can use for something else. Just one thing per layer, not two or three that conflict with one another. > I did create a VM on my laptop and recreated > as per the above and did not see the same result. If the version of fdisk you are using is smart enough, it will detect the PV signature and remove it for you: | Welcome to fdisk (util-linux 2.33.1). | Changes will remain in memory only, until you decide to write them. | Be careful before using the write command. | |!!! The old LVM2_member signature will be removed by a write command. !!! | | Device does not contain a recognized partition table. | Created a new DOS disklabel with disk identifier 0x3eb343d9. However other versions of fdisk might not do so. For example, 'busybox fdisk' does not care about the PV signature at all. As it happens to be located at a different offset, than the dos partition table, it remains and you end up in confusion. > How bad is this and can it be corrected ? 'wipefs' is a tool that searches for magic bytes and removes them. It can help you get rid of many unwanted signatures. # wipefs --no-act /dev/loop0 |DEVICE OFFSET TYPE UUID LABEL |loop0 0x218 LVM2_member Qp5dGF-gDry-WLwD-rMsY-FKl6-gKTH-0yTR2S |loop0 0x1fe dos The LVM2_member we want to be rid of is at offset 0x218 so use that... # wipefs --no-act --offset 0x218 /dev/loop0 | /dev/loop0: 8 bytes were erased at offset 0x00000218 (LVM2_member): 4c 56 4d 32 20 30 30 31 Remove the --no-act if you're happy with the result. This is the minimal invasive approach (only a few bytes erased). If you know what you're doing you can also zero out the entire area before the 1st partition, then restore the partition table. Just be careful not to delete too much. Regards Andreas Klauer
