Persistent device naming for NVMe storage devices

block-devicedevicesstorage

The Linux kernel's simple naming for a storage device (e.g. /dev/sda, /dev/sdb) can change randomly across boots. Is that true for NVMe storage devices too? These have names such as /dev/nvme0n1p1 and /dev/nvme0n1p2, etc.

Best Answer

Short: No. You can not rely on the name of the descriptor. And you most likely never will.

The NVMe naming standard describes:

nvme0: first registered device's device controller
nvme0n1: first registered device's first namespace
nvme0n1p1: first registered device's first namespace's first partition

So the overall naming is depended on your physical layout. And that can change depending on you use case by adding/removing block devices, drive failures, etc.

Basically the same as with the sd_ descriptors.

What you can rely on is the order of the listed partitions for each device, as those are getting stored on and read from the block device' partition table. As long as you do not change the partition layout, the order stays the same.

In the end, referring to either to the device UUID or PARTUUID is still the best practise, even with NVMe. Depending on the use case, referring to the LABEL might be more convenient.

Your problem would be solved if both the Pi and the powered storage device were on a UPS.

This is a common problem with /media. It will take the assigned name and begin adding digits if it hasn't cleared its cache (usually requires a reboot) before you unplug then replug (or unpower then repower the storage device).

Conversely, one thing always remains constant: The USB connection to the (first) Arduino Nano is always named /dev/ttyUSB0 and the (first) USB connection to an Arduino Uno is /dev/ttyACM0 -- They just disappear when it is unplugged then come right back when replugged.

The only way to confuse them is if you have more than one of the same type (Nano or Uno) and you replug them in a different order than was done initially.

This only matters in the Arduino IDE on the Rpi because if you have more than one of the same type there is no way to tell them apart other than knowing the order which you used to plug them in.

If you forget, then close the IDE, unplug them, then use

ls /dev/tty*

repeatedly to watch what changes as you plug them back in.

Then you can restart the IDE and they'll show up as available ports.

Linux – Given a block device, how to detect if names of partitions must contain “p”

If device name ends with digit then kernel adds 'p' symbol to separate partition number from device name.

/dev/sda -> /dev/sda1
/dev/mmcblk0 -> /dev/mmcblk0p1

For details see disk_name function in Linux kernel sources (linux/block/partition-generic.c):

if (isdigit(hd->disk_name[strlen(hd->disk_name)-1]))
    snprintf(buf, BDEVNAME_SIZE, "%sp%d", hd->disk_name, partno);
else
    snprintf(buf, BDEVNAME_SIZE, "%s%d", hd->disk_name, partno)

Best Answer

Related Solutions

Raspbian: USB storage device name changing after USB device power cycle

Your problem would be solved if both the Pi and the powered storage device were on a UPS.

Linux – Given a block device, how to detect if names of partitions must contain “p”

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