Connect to Elastic SAN Preview volumes - Linux

Article
09/12/2023

This article explains how to connect to an Elastic storage area network (SAN) volume from a Linux client. For details on connecting from a Windows client, see Connect to Elastic SAN Preview volumes - Windows.

In this article, you'll add the Storage service endpoint to an Azure virtual network's subnet, then you'll configure your volume group to allow connections from your subnet. Finally, you'll configure your client environment to connect to an Elastic SAN volume and establish a connection.

Prerequisites

Use either the latest Azure CLI or install the latest Azure PowerShell module
Deploy an Elastic SAN Preview
Configure a virtual network endpoint
Configure virtual network rules

Limitations

Currently, Elastic SAN (preview) is only available in the following regions with the following redundancies:

France Central - LRS & ZRS
Southeast Asia - LRS
Australia East - LRS
North Europe - LRS & ZRS
West Europe - LRS & ZRS
UK South - LRS
East US - LRS
South Central US - LRS
East US 2 - LRS
West US 2 - LRS & ZRS
West US 3 - LRS
Sweden Central - LRS

Connect to a volume

You can either create single sessions or multiple-sessions to every Elastic SAN volume based on your application's multi-threaded capabilities and performance requirements. To achieve higher IOPS and throughput to a volume and reach its maximum limits, use multiple sessions and adjust the queue depth and IO size as needed, if your workload allows.

When using multiple sessions, generally, you should aggregate them with Multipath I/O. It allows you to aggregate multiple sessions from an iSCSI initiator to the target into a single device, and can improve performance by optimally distributing I/O over all available paths based on a load balancing policy.

Environment setup

To create iSCSI connections from a Linux client, install the iSCSI initiator package. The exact command may vary depending on your distribution, and you should consult their documentation if necessary.

As an example, with Ubuntu you'd use sudo apt install open-iscsi, with SUSE Linux Enterprise Server (SLES) you'd use sudo zypper install open-iscsi and with Red Hat Enterprise Linux (RHEL) you'd use sudo yum install iscsi-initiator-utils.

Multipath I/O - for multi-session connectivity

Install the Multipath I/O package for your Linux distribution. The installation will vary based on your distribution, and you should consult their documentation. As an example, on Ubuntu the command would be sudo apt install multipath-tools, for SLES the command would be sudo zypper install multipath-tools and for RHEL the command would be sudo yum install device-mapper-multipath.

Once you've installed the package, check if /etc/multipath.conf exists. If /etc/multipath.conf doesn't exist, create an empty file and use the settings in the following example for a general configuration. As an example, mpathconf --enable will create /etc/multipath.conf on RHEL.

You'll need to make some modifications to /etc/multipath.conf. You'll need to add the devices section in the following example, and the defaults section in the following example sets some defaults are generally applicable. If you need to make any other specific configurations, such as excluding volumes from the multipath topology, see the main page for multipath.conf.

defaults {
    user_friendly_names yes		# To create ‘mpathn’ names for multipath devices
    path_grouping_policy multibus	# To place all the paths in one priority group
    path_selector "round-robin 0"	# To use round robin algorithm to determine path for next I/O operation
    failback immediate			# For immediate failback to highest priority path group with active paths
    no_path_retry 1			# To disable I/O queueing after retrying once when all paths are down
}
devices {
  device {
    vendor "MSFT"
    product "Virtual HD"
  }
}

After creating or modifying the file, restart Multipath I/O. On Ubuntu, the command is sudo systemctl restart multipath-tools.service and on RHEL and SLES the command is sudo systemctl restart multipathd.

Gather information

Before you can connect to a volume, you'll need to get StorageTargetIQN, StorageTargetPortalHostName, and StorageTargetPortalPort from your Azure resources.

Run the following command to get these values:

# Connect to Azure
az login

# Get volume information
az elastic-san volume show -e yourSanName -g yourResourceGroup -v yourVolumeGroupName -n yourVolumeName

You should see a list of output that looks like the following:

Note down the values for targetIQN, targetPortalHostName, and targetPortalPort, you'll need them for the next sections.

Determine sessions to create

For multi-session connections, install Multipath I/O - for multi-session connectivity.

Multi-session connections

To establish multiple sessions to a volume, first you'll need to create a single session with particular parameters.

To establish persistent iSCSI connections, modify node.startup in /etc/iscsi/iscsid.conf from manual to automatic.

Replace yourTargetIQN, yourTargetPortalHostName, and yourTargetPortalPort with the values you kept, then run the following commands from your compute client to connect an Elastic SAN volume.

sudo iscsiadm -m node --targetname yourTargetIQN --portal yourTargetPortalHostName:yourTargetPortalPort -o new

sudo iscsiadm -m node --targetname yourTargetIQN -p yourTargetPortalHostName:yourTargetPortalPort -l

Then, get the session ID and create as many sessions as needed with the session ID. To get the session ID, run iscsiadm -m session and you should see output similar to the following:

tcp:[15] <name>:port,-1 <iqn>
tcp:[18] <name>:port,-1 <iqn>

15 is the session ID we'll use from the previous example.

The following script is a loop that creates as many additional sessions as you specify. Replace numberOfAdditionalSessions with your desired number of additional sessions and replace sessionID with the session ID you'd like to use, then run the script.

sudo for i in `seq 1 numberOfAdditionalSessions`; do sudo iscsiadm -m session -r sessionID --op new; done

You can verify the number of sessions using sudo multipath -ll

When you've finished creating sessions for each of your volumes, run the following command once for each volume you'd like to maintain persistent connections to. This keeps the volume's connections active when your client reboots.

sudo iscsiadm -m node --targetname yourTargetIQN --portal yourTargetPortalHostName:yourTargetPortalPort --op update -n node.session.nr_sessions -v numberofAdditionalSessions+1

Single-session connections