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Matias Bjørling edited this page Jul 28, 2015 · 21 revisions

Requirements

Check out the Linux kernel git clone https://github.com/OpenChannelSSD/linux.git

Configure it to at least include

CONFIG_NVM=y
# Hybrid target support (required to expose a block device)
CONFIG_NVM_RRPC=y
# Hybrid block manager support (required)
CONFIG_NVM_BM_HB=y
# For null_nvm support
CONFIG_NVM_NULL_NVM=m
# For NVMe support
CONFIG_BLK_DEV_NVME=m

How to use

Open-Channel SSDs require support in the kernel. As the code is in the process of being upstreamed (lkml), a modified kernel implementing this support must be used. In order to compile the necessary modules see the requirements section.

Target administration

Add target

After the modified kernel is booted and either NVMe module or null_blk module is used, use the following command to initialize a target (FTL) on top of a open-channel compatible device.

echo "a nvme0n1 test rrpc 0:0" > /sys/module/lnvm/parameters/configure_debug

The parameters is as following:

  1. a -> Adds a target to a backend device
  2. nvme0n1 -> Backend device (use cat /sys/module/lnvm/parameters/configure_debug to see available devices).
  3. test -> Name of target to be exposed at /dev/test.
  4. rrpc -> Name of the target engine. Our case rrpc.
  5. 0:0 is start channel : end channel. This is a range of how many channels of the attached open-channel SSD device that should be allocated to the target.

After successfully registering the target. You may issue reads and writes to /dev/mytarget.

Delete target

echo "d test" > /sys/module/lnvm/parameters/configure_debug

deletes the configured "test" target.

List block information on backend device

echo "s nvme0n1" > /sys/module/lnvm/parameters/configure_debug

List's the internal information of a target.

Initialize using null_blk driver

Instantiate the module with the following parameters

queue_mode=2 gb=4 nr_devices=1 nvm_enable=1 nvm_num_channels=1

That will instantiate the LightNVM driver with a 4GB SSD, with a single channel. You can see that it was instantiated by checking the kernel log.

dmesg |grep nvm

where the output should be similar to

[    2.120740] nvm: registered nulln0 with luns: 1 blocks: 2048 sector size: 4096
[    2.325021] nvm: registered nvme0n1 with luns: 1 blocks: 2044 sector size: 4096
[  188.228560] nvm: rrpc initialized with 1 luns and 261632 pages.

Instantiate NVMe driver using QEMU

If you have a LightNVM-compatible device, simply plug it in and it should be found. If you don't, then you can use the LightNVM-enabled QEMU branch to prototype with.

It's based on top of Keith Busch's qemu-nvme branch that implements an NVMe compatible device.

QEMU Installation

Clone the qemu source from

git clone https://github.com/OpenChannelSSD/qemu-nvme.git

and configure the QEMU source with

./configure --enable-linux-aio --target-list=x86_64-softmmu --enable-kvm

then make and install

Configure QEMU

Create an empty file to hold your NVMe device.

dd if=/dev/zero of=blknvme bs=1M count=1024

this creates a zeroed 1GB file called "blknvme". From there, you can boot your favorite Linux image with

qemu-system-x86_64 -m 4G -smp 1,cores=4 --enable-kvm 
-hda YourLinuxVMFile -append "root=/dev/sda1"
-kernel "/home/foobar/git/linux/arch/x86_64/boot/bzImage"
-drive file=blknvme,if=none,id=mynvme
-device nvme,drive=mynvme,serial=deadbeef,namespaces=1,lver=1,lchannels=1,nlbaf=5,lba_index=3,mdts=10

Where you replace YourLinuxVMFile with your preinstalled Linux virtual machine. LightNVM is enabled with lver=1. The number of LightNVM channels is set to one, and the last part defines the page size to be 4K.

QEMU support the following LightNVM-specific parameters:

- lver=<int>       : version of the LightNVM standard to use, Default:1
- ltype=<nvmtype>  : Whether device is block- or byte addressable, Default:0 (block)
- lchannels=<int>    : Number of channels per namespace, Default: 4
- lreadl2ptbl=<int>  : Load logical to physical table. 1: yes, 0: no. Default: 1
- lbbtable=<file>    : Load bad block table from file destination (Provide path to file. If no file is provided a bad block table will be generation. Look at lbbfrequency. Default: Null (no file).
- lbbfrequency:<int> : Bad block frequency for generating bad block table. If no frequency is provided LNVM_DEFAULT_BB_FREQ will be used.

The list of LightNVM parameters in QEMU can be found in $QUEMU_DIR/hw/block/nvme.c under the Advanced optional options comment.

Common Problems

Kernel panic on boot using NVMe

  1. Zero out your nvme backend file. dd if=/dev/zero of=backend_file bs=1M count=X

  2. Remember to upgrade the qemu-nvme branch as well. The linux and qemu-nvme repos follow each other.

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