LVMs with mixed block sizes break subiquity

[Christian Ehrhardt ]

Hi,
I was trying to create the following setup.

2* DASD (4K block size by default) and 2*FCP (512b block size) into a single LVM.

That crashed subiquity badly and I have selected "submit to Canonical" but fail to get any feedback where that data is. I have since then rebooted, but if you could help to combine this report and the data that would be great.

I later on tried to combine such an LVM manually and found a possible root cause:
 sudo vgextend ubuntu-vg /dev/dasdf1 /dev/mapper/mpathd-part1 /dev/mapper/mpathe-part1
   Devices have inconsistent logical block sizes (4096 and 512).

So it seems subiquity/curtin need to better consider/adapt block sizes (re-format dasd devices for example) to make them match each other to be able to create a single LVM across them.

[Christian Ehrhardt  (paelzer)]

As confirmation to prove that it can work.
After re-formatting the dasd blksize to match the 512 of the fcp disks as following I was able to "unite" them in one LVM.

$ sudo dasdfmt /dev/disk/by-path/ccw-0.0.254e
[sudo] password for ubuntu:
Please enter the blocksize of the formatting [4096]: 512
Drive Geometry: 60102 Cylinders * 15 Heads = 901530 Tracks
Device Type: Fully Provisioned
I am going to format the device /dev/disk/by-path/ccw-0.0.254e in the following way:
   Device number of device : 0x254e
   Labelling device : yes
   Disk label : VOL1
   Disk identifier : 0X254E
   Extent start (trk no) : 0
   Extent end (trk no) : 901529
   Compatible Disk Layout : yes
   Blocksize : 512
   Mode : Full
...

$ sudo fdasd /dev/disk/by-path/ccw-0.0.254e
...
$ lsdasd | grep 512
0.0.154e active dasdc 94:8 ECKD 512 21569MB 44174970
0.0.254e active dasdf 94:20 ECKD 512 21569MB 44174970

$ sudo pvcreate /dev/disk/by-path/ccw-0.0.254e-part1
$ sudo pvcreate /dev/disk/by-path/ccw-0.0.154e-part1
$ sudo vgextend ubuntu-vg /dev/disk/by-path/ccw-0.0.254e-part1 /dev/disk/by-path/ccw-0.0.154e-part1
  Volume group "ubuntu-vg" successfully extended
$ sudo lvextend /dev/ubuntu-vg/ubuntu-lv /dev/disk/by-path/ccw-0.0.254e-part1 /dev/disk/by-path/ccw-0.0.154e-part1
  Size of logical volume ubuntu-vg/ubuntu-lv changed from 126.99 GiB (32510 extents) to <169.12 GiB (43294 extents).
  Logical volume ubuntu-vg/ubuntu-lv successfully resized.

[Michael Hudson-Doyle (mwhudson)]

I'm a little confused here. Are you saying that you tried to combine the dasd and fcp drives into a single vg and things exploded? I guess subiquity should read out the physical block size of each device and prevent combinations that will not work...

[Christian Ehrhardt  (paelzer)]

Yes Michael you are reading correctly, that is exactly what I tried and what happened.

I agree in "general" that "read the phys block size and prevent that config" would be a good start.

But Dasd's in there have a special twist as they don't really have blocks anyway (they have tracks and records), so with a dasdfmt call you can essentially "change" the physical block size (there is a net-size vs granularity tradeoff but anyway I have shown above that it can work).