Thanks very much. Will look into that. Not familiar with MD devices and this was short notice and urgent. A lesson for next time I guess. Regards On Fri, Jan 18, 2019 at 2:23 PM Andreas Klauer <Andreas.Klauer@xxxxxxxxxxxxxx> wrote: > > 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
