Storage Over TCP in a Flash

By Patrick Dehkordi

Recently Solarflare delivered a TCP transport for Non-Volatile Memory Express (NVMe). The big deal with NVMe is that it’s FLASH memory based, and often multi-ported so when these “disk blocks” are transferred over the network, even with TCP, they often arrive 100 times faster than they would if they were coming off spinning media. We’re talking 100 microseconds versus average 15K RPM disk seek times measured in milliseconds. Unlike RoCE or iWARP a TCP transport provides storage over Ethernet without requiring ANY network infrastructure changes.

It should be noted that this should work for ANY NIC and does not require RDMA, RoCE, iWARP or any special NIC offload technology. Furthermore, since this is generic TCP/IP over Ethernet you don’t need to touch your switches to setup Data Center Bridging. Also, you don’t need Data Center Ethernet, Converged Ethernet, or Converged Enhanced Ethernet, just plain old Ethernet.  Nor do you need to set things up to use Pause Frames, or Priority Flow Control. This is industry changing stuff, and yet not hard to implement for testing so I’ve included a recipe for how to make this function in your lab below, it is also cross posted in the GitHub.

At present this is a fork of the v4.11 kernel. This adds two new kconfig options:

  • NVME_TCP : enable initiator support
  • NVME_TARGET_TCP : enable target support

The target requires the nvmet module to be loaded. Configuration is identical to RDMA, except "tcp" should be used for addr_trtype.

The host requires the nvme, nvme_core and nvme_fabrics modules to be loaded. Again, configuration is identical to RDMA, except -t tcp should be passed to the nvme command line utility instead of -t rdma. This requires a patched version of nvme-cli.

Example assumptions

This is assuming a target IP of, a subsytem name of ramdisk and an underlying block device /dev/ram0. This is further assuming an existing system with RedHat/Centos Distribution built on 3.x kernel.

Building the Linux kernel

For more info refer to:

Install or confirm the following packages are installed

yum install gcc make git ctags ncurses-devel openssl-devel

Download, unzip or clone the repo into a local directory

git clone
cd nvme-of-tcp-4.11

Create a .config file or copy the existing .config file into the build directory

scp /boot/config-3.10.0-327.el7.x86_64 .config

Modify the .config to include the relevant NVMe modules

make menuconfig

Under “Block Devices” at a minimum select “NVM Express block device” “NVMe over Fabrics TCP host support” “NVMe over Fabrics TCP target support” Save and Exit the text based kernel configuration utility.

Confirm the changes

grep NVME_ .config

Compile and install the kernel

(To save time you can utilize multiple CPUs by including the j option)

make -j 16
make -j 16 modules_install install 

Confirm that the build is included in the boot menu entry

(This is dependent on the bootloader being used, for GRUB2)

cat /boot/grub2/grub.cfg | grep menuentry

Set the build as the default boot option

grub2-set-default 'Red Hat Enterprise Linux Server (4.11.0) 7.x (Maipo)’

Reboot the system


Confirm that the kernel has been updated:

uname -a 
Linux 4.11.0 #1 SMP date  x86_64 GNU/Linux

NVMe CLI Update

Download the correct version of the NVMe CLI utility that includes TCP:

git clone

Update the NVMe CLI utility:

cd nvme-cli
make install

Target setup

Load the target driver

This should automatically load the dependencies,nvmenvme_core and nvme_fabrics

modprobe nvmet_tcp

Set up storage subsystem

mkdir /sys/kernel/config/nvmet/subsystems/ramdisk
echo 1 > /sys/kernel/config/nvmet/subsystems/ramdisk/attr_allow_any_host
mkdir /sys/kernel/config/nvmet/subsystems/ramdisk/namespaces/1
echo -n /dev/ram0 > /sys/kernel/config/nvmet/subsystems/ramdisk/namespaces/1/device_path
echo 1 > /sys/kernel/config/nvmet/subsystems/ramdisk/namespaces/1/enable

Setup port

mkdir /sys/kernel/config/nvmet/ports/1
echo "ipv4" > /sys/kernel/config/nvmet/ports/1/addr_adrfam
echo "tcp" > /sys/kernel/config/nvmet/ports/1/addr_trtype
echo "11345" > /sys/kernel/config/nvmet/ports/1/addr_trsvcid
echo "" > /sys/kernel/config/nvmet/ports/1/addr_traddr

Associate subsystem with port

ln -s /sys/kernel/config/nvmet/subsystems/ramdisk /sys/kernel/config/nvmet/ports/1/subsystems/ramdisk

Initiator setup

Load the initiator driver

This should automatically load the dependencies,nvmenvme_core and nvme_fabrics.

modprobe nvme_tcp

Use the NVMe CLI utility to connect the initiator to the target:

nvme connect -t tcp -a -s 11345 -n ramdisk

lsblk should now show an NVMe device.