Understanding plain Linux NVMe device names (in
/dev and kernel messages)
On Linux, plain disk names for most modern disk devices are in
/dev/sda for the whole disk and
/dev/sda3 for the
partition (regardless of whether the disk is partitioned through
or old MBR). When I got NVMe SSDs for my office workstation, one of my many discoveries about them is
that Linux gives them different and more oddly formed names. Since I
had many other NVMe related issues on my mind at the time, I didn't look
into the odd names; I just accepted them and moved on. But now I want
to actually understand how Linux's NVMe device names are formed and
what they mean, and it turns out to be relatively simple.
Let's start with the actual names. On Linux, NVMe devices have three
levels of names. On my office workstation, for the first NVMe device
/dev/nvme0n1, and then a series of
/dev/nvme0n1p<X> devices for each partition. Unusually,
is a character device, not a block device. Kernel messages will talk
about both '
nvme0' and '
nvme nvme0: pci function 0000:01:00.0 nvme nvme0: 15/0/0 default/read/poll queues nvme0n1: p1 p2 p3 p4 p5
(I don't know yet what names will appear in kernel messages about IO errors.)
If I want to partition the disk, install GRUB bootblocks, or the like,
I want to use the '
nvme0n1' name. Querying certain sorts of NVMe
information is done using '
nvme0'. I can apparently use either name
for querying SMART information with
Numbering NVMe SSDs instead of giving them letters and naming
partitions with '
p<X>' instead of plain numbers are both sensible
changes from the somewhat arcane
sd... naming scheme. The unusual
thing is the '
n1' in the middle. This is present because of a
NVMe feature called "namespaces",
which allows you (or someone) to divide up a NVMe SSD into multiple
separate ranges of logical block addresses that are isolated from
each other. Namespaces are numbered starting from one, and I think
that most NVMe drives have only one, hence '
nvme0n1' as the base
name for my first NVMe SSD's disk devices.
(This is also likely part of why '
nvme0' is a character device instead
of a block device. Although I haven't checked the NVMe specification,
I suspect that you can't read or write blocks from a NVMe SSD without
specifying the namespace.)
The Arch wiki page on NVMe drives has a nice
overview of all sorts of things you can find out about your NVMe drives
nvme command. Based on the Arch
nvme manpage, it has a lot of sub-commands
For my expected uses, I suspect that I will never change or manipulate NVMe namespaces on my NVMe drives. I'll just leave them in their default state, as shipped by the company making them. Probably all consumer NVMe SSDs will come with only a single namespace by default, so that people can use the entire drive's official capacity as a single filesystem or partition without having to do strange things.