What's the difference between /dev/sg0 and /dev/sr0?

Question

$ uname -srvmpio
Linux 5.4.0-31-generic #35-Ubuntu SMP Thu May 7 20:20:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$ sudo cdrecord -inq
Device was not specified. Trying to find an appropriate drive...
Detected CD-R drive: /dev/cdrw
Using /dev/cdrom of unknown capabilities
Device type    : Removable CD-ROM
Version        : 5
Response Format: 2
Capabilities   : 
Vendor_info    : 'TSSTcorp'
Identification : 'DVD+-RW SU-208GB'
Revision       : 'D100'
Device seems to be: Generic mmc2 DVD-R/DVD-RW.
$ sudo cdrecord --devices
wodim: Overview of accessible drives (1 found) :
-------------------------------------------------------------------------
 0  dev='/dev/sg1'      rwrw-- : 'TSSTcorp' 'DVD+-RW SU-208GB'
-------------------------------------------------------------------------
$ ls -la /dev/cdrw /dev/sg1 /dev/sr0
lrwxrwxrwx  1 root root      3 Mai 20 19:44 /dev/cdrw -> sr0
crw-rw----+ 1 root cdrom 21, 1 Mai 20 19:44 /dev/sg1
brw-rw----+ 1 root cdrom 11, 0 Mai 20 19:44 /dev/sr0

So, what's the difference between /dev/sg1 and /dev/sr0? Which one to use for burning data DVDs? The machine has only one physical CD/DVD drive.

Moreover: can this drive write double-layered DVDs?

Solution

These are naming conventions for SCSI drivers. Below are some of the SCSI drivers:

• sd: mass-storage driver
  • sda: first registered device
  • sdb, sdc, etc.: second, third, etc. registered devices
• ses: Enclosure driver
• sg: generic SCSI layer
• sr: “ROM” driver (data-oriented optical disc drives; scd is just a secondary alias)
• st: magnetic tape driver

Source: Naming conventions - Device file - Wikipedia

Additionally, Generic SCSI just gives the guest operating system direct access to SCSI devices connected to the host. So, you're actually using /dev/sr0 for burning DVD.