numam-spdk/doc/iscsi.md

iSCSI Target

iSCSI Target Getting Started Guide

The Storage Performance Development Kit iSCSI target application is named iscsi_tgt. This following section describes how to run iscsi from your cloned package.

Prerequisites

This guide starts by assuming that you can already build the standard SPDK distribution on your platform.

Once built, the binary will be in app/iscsi_tgt.

If you want to kill the application by using signal, make sure use the SIGTERM, then the application will release all the shared memory resource before exit, the SIGKILL will make the shared memory resource have no chance to be released by applications, you may need to release the resource manually.

Introduction

The following diagram shows relations between different parts of iSCSI structure described in this document.

Configuring iSCSI Target via config file

A iscsi_tgt specific configuration file is used to configure the iSCSI target. A fully documented example configuration file is located at etc/spdk/iscsi.conf.in.

The configuration file is used to configure the SPDK iSCSI target. This file defines the following: TCP ports to use as iSCSI portals; general iSCSI parameters; initiator names and addresses to allow access to iSCSI target nodes; number and types of storage backends to export over iSCSI LUNs; iSCSI target node mappings between portal groups, initiator groups, and LUNs.

You should make a copy of the example configuration file, modify it to suit your environment, and then run the iscsi_tgt application and pass it the configuration file using the -c option. Right now, the target requires elevated privileges (root) to run.

app/iscsi_tgt/iscsi_tgt -c /path/to/iscsi.conf

Assigning CPU Cores to the iSCSI Target

SPDK uses the DPDK Environment Abstraction Layer to gain access to hardware resources such as huge memory pages and CPU core(s). DPDK EAL provides functions to assign threads to specific cores. To ensure the SPDK iSCSI target has the best performance, place the NICs and the NVMe devices on the same NUMA node and configure the target to run on CPU cores associated with that node. The following command line option is used to configure the SPDK iSCSI target:

-m 0xF000000

This is a hexadecimal bit mask of the CPU cores where the iSCSI target will start polling threads. In this example, CPU cores 24, 25, 26 and 27 would be used.

Configuring a LUN in the iSCSI Target

Each LUN in an iSCSI target node is associated with an SPDK block device. See @ref bdev for details on configuring SPDK block devices. The block device to LUN mappings are specified in the configuration file as:

[TargetNodeX]
  LUN0 Malloc0
  LUN1 Nvme0n1

This exports a malloc'd target. The disk is a RAM disk that is a chunk of memory allocated by iscsi in user space. It will use offload engine to do the copy job instead of memcpy if the system has enough DMA channels.

Configuring iSCSI Target via RPC method

In addition to the configuration file, the iSCSI target may also be configured via JSON-RPC calls. See @ref jsonrpc for details.

Portal groups

• add_portal_group -- Add a portal group.
• delete_portal_group -- Delete an existing portal group.
• add_pg_ig_maps -- Add initiator group to portal group mappings to an existing iSCSI target node.
• delete_pg_ig_maps -- Delete initiator group to portal group mappings from an existing iSCSI target node.
• get_portal_groups -- Show information about all available portal groups.

/path/to/spdk/scripts/rpc.py add_portal_group 1 10.0.0.1:3260

Initiator groups

• add_initiator_group -- Add an initiator group.
• delete_initiator_group -- Delete an existing initiator group.
• add_initiators_to_initiator_group -- Add initiators to an existing initiator group.
• get_initiator_groups -- Show information about all available initiator groups.

/path/to/spdk/scripts/rpc.py add_initiator_group 2 ANY 10.0.0.2/32

Target nodes

• construct_target_node -- Add a iSCSI target node.
• delete_target_node -- Delete a iSCSI target node.
• target_node_add_lun -- Add an LUN to an existing iSCSI target node.
• get_target_nodes -- Show information about all available iSCSI target nodes.

/path/to/spdk/scripts/rpc.py construct_target_node Target3 Target3_alias MyBdev:0 1:2 64 -d

Configuring iSCSI Initiator

The Linux initiator is open-iscsi.

Installing open-iscsi package Fedora:

yum install -y iscsi-initiator-utils

Ubuntu:

apt-get install -y open-iscsi

Setup

Edit /etc/iscsi/iscsid.conf

node.session.cmds_max = 4096
node.session.queue_depth = 128

iscsid must be restarted or receive SIGHUP for changes to take effect. To send SIGHUP, run:

killall -HUP iscsid

Recommended changes to /etc/sysctl.conf

net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 0

net.ipv4.tcp_rmem = 10000000 10000000 10000000
net.ipv4.tcp_wmem = 10000000 10000000 10000000
net.ipv4.tcp_mem = 10000000 10000000 10000000
net.core.rmem_default = 524287
net.core.wmem_default = 524287
net.core.rmem_max = 524287
net.core.wmem_max = 524287
net.core.optmem_max = 524287
net.core.netdev_max_backlog = 300000

Discovery

Assume target is at 10.0.0.1

iscsiadm -m discovery -t sendtargets -p 10.0.0.1

Connect to target

iscsiadm -m node --login

At this point the iSCSI target should show up as SCSI disks. Check dmesg to see what they came up as.

Disconnect from target

iscsiadm -m node --logout

Deleting target node cache

iscsiadm -m node -o delete

This will cause the initiator to forget all previously discovered iSCSI target nodes.

Finding /dev/sdX nodes for iSCSI LUNs

iscsiadm -m session -P 3 | grep "Attached scsi disk" | awk '{print $4}'

This will show the /dev node name for each SCSI LUN in all logged in iSCSI sessions.

Tuning

After the targets are connected, they can be tuned. For example if /dev/sdc is an iSCSI disk then the following can be done: Set noop to scheduler

echo noop > /sys/block/sdc/queue/scheduler

Disable merging/coalescing (can be useful for precise workload measurements)

echo "2" > /sys/block/sdc/queue/nomerges

Increase requests for block queue

echo "1024" > /sys/block/sdc/queue/nr_requests

Example: Configure simple iSCSI Target with one portal and two LUNs

Assuming we have one iSCSI Target server with portal at 10.0.0.1:3200, two LUNs (Malloc0 and Malloc), and accepting initiators on 10.0.0.2/32, like on diagram below:

Configure iSCSI Target

Start iscsi_tgt application:

$ ./app/iscsi_tgt/iscsi_tgt

Construct two 64MB Malloc block devices with 512B sector size "Malloc0" and "Malloc1":

$ ./scripts/rpc.py bdev_malloc_create -b Malloc0 64 512
$ ./scripts/rpc.py bdev_malloc_create -b Malloc1 64 512

Create new portal group with id 1, and address 10.0.0.1:3260:

$ ./scripts/rpc.py add_portal_group 1 10.0.0.1:3260

Create one initiator group with id 2 to accept any connection from 10.0.0.2/32:

$ ./scripts/rpc.py add_initiator_group 2 ANY 10.0.0.2/32

Finally construct one target using previously created bdevs as LUN0 (Malloc0) and LUN1 (Malloc1) with a name "disk1" and alias "Data Disk1" using portal group 1 and initiator group 2.

$ ./scripts/rpc.py construct_target_node disk1 "Data Disk1" "Malloc0:0 Malloc1:1" 1:2 64 -d

Configure initiator

Discover target

$ iscsiadm -m discovery -t sendtargets -p 10.0.0.1
10.0.0.1:3260,1 iqn.2016-06.io.spdk:disk1

Connect to the target

$ iscsiadm -m node --login

At this point the iSCSI target should show up as SCSI disks.

Check dmesg to see what they came up as. In this example it can look like below:

...
[630111.860078] scsi host68: iSCSI Initiator over TCP/IP
[630112.124743] scsi 68:0:0:0: Direct-Access     INTEL    Malloc disk      0001 PQ: 0 ANSI: 5
[630112.125445] sd 68:0:0:0: [sdd] 131072 512-byte logical blocks: (67.1 MB/64.0 MiB)
[630112.125468] sd 68:0:0:0: Attached scsi generic sg3 type 0
[630112.125926] sd 68:0:0:0: [sdd] Write Protect is off
[630112.125934] sd 68:0:0:0: [sdd] Mode Sense: 83 00 00 08
[630112.126049] sd 68:0:0:0: [sdd] Write cache: enabled, read cache: disabled, doesn't support DPO or FUA
[630112.126483] scsi 68:0:0:1: Direct-Access     INTEL    Malloc disk      0001 PQ: 0 ANSI: 5
[630112.127096] sd 68:0:0:1: Attached scsi generic sg4 type 0
[630112.127143] sd 68:0:0:1: [sde] 131072 512-byte logical blocks: (67.1 MB/64.0 MiB)
[630112.127566] sd 68:0:0:1: [sde] Write Protect is off
[630112.127573] sd 68:0:0:1: [sde] Mode Sense: 83 00 00 08
[630112.127728] sd 68:0:0:1: [sde] Write cache: enabled, read cache: disabled, doesn't support DPO or FUA
[630112.128246] sd 68:0:0:0: [sdd] Attached SCSI disk
[630112.129789] sd 68:0:0:1: [sde] Attached SCSI disk
...

You may also use simple bash command to find /dev/sdX nodes for each iSCSI LUN in all logged iSCSI sessions:

$ iscsiadm -m session -P 3 | grep "Attached scsi disk" | awk '{print $4}'
sdd
sde

iSCSI Hotplug

At the iSCSI level, we provide the following support for Hotplug:

1. bdev/nvme: At the bdev/nvme level, we start one hotplug monitor which will call spdk_nvme_probe() periodically to get the hotplug events. We provide the private attach_cb and remove_cb for spdk_nvme_probe(). For the attach_cb, we will create the block device base on the NVMe device attached, and for the remove_cb, we will unregister the block device, which will also notify the upper level stack (for iSCSI target, the upper level stack is scsi/lun) to handle the hot-remove event.

2. scsi/lun: When the LUN receive the hot-remove notification from block device layer, the LUN will be marked as removed, and all the IOs after this point will return with check condition status. Then the LUN starts one poller which will wait for all the commands which have already been submitted to block device to return back; after all the commands return back, the LUN will be deleted.

Known bugs and limitations

For write command, if you want to test hotplug with write command which will cause r2t, for example 1M size IO, it will crash the iscsi tgt. For read command, if you want to test hotplug with large read IO, for example 1M size IO, it will probably crash the iscsi tgt.

@sa spdk_nvme_probe