Managing Nvme Namespaces

Manage your nvme device

We explore how to manage your nvme device here.

NVMe Overview

NVM Express is a scalable host controller interface designed to address the needs of Enterprise, Data Center and Client systems that utilize PCI Express® (PCIe®) based solid state drives. NVM Express specifications are owned and maintained by NVM Express, Inc.

NVMe device is managed by a user space tooling, nvme-cli for Linux. Continue reading to find out how to manage and start using your NVMe device, using nvme-cli.

What is nvme namespace

Let us not get bored by giving information that can be found elsewhere easily. NVMe device is addressed as nvmeX in linux, found at /dev. The nvmeX is a character device and can have one or many block devices (referred to as namespaces).

# ls -l /dev/nvme*
crw-------. 1 root root 243,  0 Oct  3 14:43 /dev/nvme0
brw-rw----. 1 root disk 259,  0 Oct  3 14:43 /dev/nvme0n1
brw-rw----. 1 root disk 259,  0 Oct  3 14:43 /dev/nvme0n2

The block devices can be viewed using the command nvme list, as below:

# nvme list
Node             SN     Model                       Namespace Usage                      Format         FW Rev  
---------------- ------ --------------------------- --------- -------------------------- -------------- ----------
/dev/nvme0n1     SN     1.6TB NVMe Gen4 U.2 SSD     1         25.00  GB /  25.00  GB     4 KiB +  0 B   FW Version
/dev/nvme0n2     SN     1.6TB NVMe Gen4 U.2 SSD     2         25.00  GB /  25.00  GB     4 KiB +  0 B   FW Version

Basic commands of nvme-cli to control the namespaces of nvme device

To find capacity of an NVMe device:

# nvme id-ctrl /dev/nvme0 | grep -i tnvmcap
tnvmcap   : 1600321314816

This means it is a 1.6 TB Device

To find number of namespaces an NVMe device supports:

# nvme id-ctrl /dev/nvme0 | grep ^nn
nn        : 64

which means it supports 64 namespaces

Block size of NVMe device:

# nvme id-ns /dev/nvme0n1 | grep "in use"
lbaf  0 : ms:0   lbads:12 rp:0 (in use)

This means the block size of nvme device is 2^12, which is 4096

So, max number of blocks the device supports is:

# expr 1600321314816 / 4096
390703446

Managing namespaces of nvme device

We need to know the controller ID of the nvme device

# # nvme id-ctrl /dev/nvme0 | grep ^cntlid
cntlid    : 0x41

We need to decide what is the size of the namespace we are going to create. Let us divide 390703446 by 64. We get 6104741, which will be size of one namespace (assuming we create identical 64 namespaces).

We need to create namespace, and then attach it to the controller via the controller ID.

# nvme create-ns /dev/nvme0 --nsze=6104741 --ncap=6104741 --flbas=0 -dps=0
create-ns: Success, created nsid:1

# nvme attach-ns /dev/nvme0 --namespace-id=1 -controllers=0x41
attach-ns: Success, nsid:1

# nvme list
Node             SN     Model                       Namespace Usage                      Format         FW Rev  
---------------- ------ --------------------------- --------- -------------------------- -------------- ----------
/dev/nvme0n1     SN     1.6TB NVMe Gen4 U.2 SSD     1         25.00  GB /  25.00  GB     4 KiB +  0 B   FW Version

We can do this multiple times, by running create-ns multiple times and varying the namespace id in the attach-ns command

Check out a bash script to do this here

Now, this namespace can be used like any block device.

# lsblk /dev/nvme0n1
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
nvme0n1 259:5    0  14G  0 disk

To delete this namespace:

# nvme delete-ns /dev/nvme0 -n 1
delete-ns: Success, deleted nsid:1

Now we are ready to play with our nvme devices.