numam-spdk/doc/iscsi.md

iSCSI Target

iSCSI Target Getting Started Guide

The Intel(R) 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. The SPDK iSCSI target has been known to work on several Linux distributions, namely Ubuntu 14.04, 15.04, and 15.10, Fedora 21, 22, and 23, and CentOS 7.

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.

Configuring iSCSI Target

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.

Each LUN in an iSCSI target node is associated with an SPDK block device. See @ref bdev_getting_started 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.

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

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 192.168.1.5

iscsiadm -m discovery -t sendtargets -p 192.168.1.5

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

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