While preparing a presentation for POUG 2025 I had a need to find out more about the block device driver in use on my system. I was particularly interested in the SCSI mid-layer and low-layer drivers. Unsure about these terms? I am referring to the Linux Storage Stack Diagram. It’s a great resource for anyone interested in the Linux block layer.

Naturally it all depends, but the simplest way I found of identifying the driver for a given block device is lsblk. On my test VM, running Oracle Linux 9.6/x86-64, this is what’s reported.

$ lsblk -o name,maj:min,rm,size,ro,type,mountpoints,subsystems
NAME                    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS SUBSYSTEMS
vda                     251:0    0   20G  0 disk             block:virtio:pci
├─vda1                  251:1    0    1G  0 part /boot       block:virtio:pci
└─vda2                  251:2    0   19G  0 part             block:virtio:pci
  ├─ol_ol9packer-root   252:0    0   17G  0 lvm  /           block
  └─ol_ol9packer-swap   252:1    0    2G  0 lvm  [SWAP]      block
vdb                     251:16   0  100G  0 disk             block:virtio:pci
└─vdb1                  251:17   0  100G  0 part             block:virtio:pci
  └─oracle_vg-oracle_lv 252:2    0  100G  0 lvm  /u01        block
vdc                     251:32   0   25G  0 disk             block:virtio:pci
└─vdc1                  251:33   0   25G  0 part             block:virtio:pci
vdd                     251:48   0   10G  0 disk             block:virtio:pci
└─vdd1                  251:49   0   10G  0 part             block:virtio:pci

If you’ve been working with KVM/qemu before this looks quite familiar. The VM in question uses block devices attached to the virtio bus. By definition they are known as vdX devices.

By the way, if you see this …

$ lsblk -o name,maj:min,rm,size,ro,type,mountpoints,subsystems
NAME                  MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS SUBSYSTEMS
sda                     8:0    0  20G  0 disk             block:scsi:virtio:pci
├─sda1                  8:1    0   1G  0 part /boot       block:scsi:virtio:pci
└─sda2                  8:2    0  19G  0 part             block:scsi:virtio:pci
  ├─ol_ol9base-root   252:0    0  17G  0 lvm  /           block
  └─ol_ol9base-swap   252:1    0   2G  0 lvm  [SWAP]      block

… your block devices are attached to a SCSI controller using the virtio-scsi model. This is common for compute VMs in Oracle Cloud Infrastructure if you opt for a paravirtualised volume attachment.

I hope this saved you a minute or two.