LVM and device mapper: Logical Volume device sector size

This seems to be a problem regarding the sector size of the mapped device for a logical volume between different machines. More specifically, I'd like to know if and how the sector size of a mapped device corresponding to a logical volume can be configured. Here is a description of the problem, comparing two machines. ## Machine 1 I have an entire disk image in a logical volume mytestlv in a volume group named MyVolumeGroup. This disk image has its own partition table (completely independent of the actual disk it's stored on). For example, fdisk /dev/mapper/MyVolumeGroup-mytestlv shows this:

Disk /dev/mapper/MyVolumeGroup-mytestlv: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: ...

Device                                    Start      End  Sectors Size Type
/dev/mapper/MyVolumeGroup-mytestlv-part1    2048     4095     2048   1M BIOS boot
/dev/mapper/MyVolumeGroup-mytestlv-part2    4096  4198399  4194304   2G Linux swap
/dev/mapper/MyVolumeGroup-mytestlv-part3 4198400 62914526 58716127  28G Linux filesystem

If I need access to the data on a partition of that disk image, I can use kpartx and mount the partition. kpartx -a /dev/mapper/MyVolumeGroup-mytestlv creates these devices files, which can be used to mount a partition within that disk image, for example:

/dev/mapper/MyVolumeGroup-mytestlvl
/dev/mapper/MyVolumeGroup-mytestlv2
/dev/mapper/MyVolumeGroup-mytestlv3

## Machine 2 This was now copied onto a different machine (content is exactly the same, checksums of both entire /dev/mapper/MyVolumeGroup-mytestlv are identical). Using the configured block size, fdisk /dev/mapper/MyVolumeGroup-mytestlv shows this:

/dev/mapper/MyVolumeGroup-mytestlv: 30 GiB, 32212254720 bytes, 7864320 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device                                  Boot Start     End Sectors Size Id Type
/dev/mapper/MyVolumeGroup-mytestlv-part1          1 7864319 7864319  30G ee GPT

## Differences The logical sector size is 512 on Machine 1, but 4096 on Machine 2. On Machine 1, blockdev --getss /dev/mapper/MyVolumeGroup-mytestlv returns 512. On Machine 2, blockdev --getss /dev/mapper/MyVolumeGroup-mytestlv returns 4096. ## Workaround On Machine 2, forcing the sector size to 512 with fdisk helps it see the partition table correctly.

fdisk --sector-size 512 /dev/mapper/MyVolumeGroup-mytestlv

Disk /dev/mapper/MyVolumeGroup-mytestlv: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: ...

Device                                    Start      End  Sectors Size Type
/dev/mapper/MyVolumeGroup-mytestlv-part1    2048     4095     2048   1M BIOS boot
/dev/mapper/MyVolumeGroup-mytestlv-part2    4096  4198399  4194304   2G Linux swap
/dev/mapper/MyVolumeGroup-mytestlv-part3 4198400 62914526 58716127  28G Linux filesystem

Unfortunately, other tools such as sfdisk or kpartx don't seem to have those options. If I create a loopback device explicitly from that LV, then that loopback device has a sector size of 512, and everything works (in fact, versions of losetup that are not too old have an explicit sector size option). After losetup --show -f /dev/mapper/MyVolumeGroup-mytestlv: * blockdev --getss /dev/loop0 returns 512 * kpartx -a /dev/loop0 creates /dev/mapper/loop0p{1,2,3} ## Where is that sector size configured? I'd like to be able to use fdisk, sfdisk, kpartx without relying on an additional losetup. On Machine 2, cat /sys/block/dm-2/queue/hw_sector_size returns 4096 (/dev/mapper/MyVolumeGroup-mytestlv is actually a soft-link to /dev/dm-2). I've tried to change this using echo 512 > /sys/block/dm-2/queue/hw_sector_size, but this doesn't seem to be possible. * Is there a way to tell LVM that I'd like the sector size for the device corresponding to /dev/mapper/MyVolumeGroup-mytestlv to be 512? * Is that something that affects all the logical volumes in the group or on the system? I can't see any options with lvcreate or lvdisplay related to this.