Connect to Elastic SAN volumes - Linux

This article explains how to connect to an Elastic SAN volume from an individual Linux client. For details on connecting from a Windows client, see Connect to Elastic SAN volumes - Windows.

In this article, you configure your volume group to allow connections from your subnet. Then, you configure your client environment to connect to an Elastic SAN volume and establish a connection.

You must use a cluster manager when connecting an individual elastic SAN volume to multiple clients. For details, see Use clustered applications on Azure Elastic SAN.

Prerequisites

• Use either the latest Azure CLI or install the latest Azure PowerShell module
• Deploy an Elastic SAN
• Either configure private endpoints or configure service endpoints

Enable iSCSI Initiator

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

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

Install Multipath I/O

To get higher IOPS and throughput to a volume and reach its maximum limits, create multiple sessions from the iSCSI initiator to the target volume based on your application's multithreaded capabilities and performance requirements. Use Multipath I/O to aggregate these multiple paths into a single device and improve performance by optimally distributing I/O over all available paths based on a load balancing policy.

Install the Multipath I/O package for your Linux distribution. The installation process varies based on your distribution, so consult their documentation. For example, on Ubuntu, use the command sudo apt install multipath-tools. On SLES, use sudo zypper install multipath-tools. On RHEL, use sudo yum install device-mapper-multipath.

After installing 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. For example, mpathconf --enable creates /etc/multipath.conf on RHEL.

Modify /etc/multipath.conf. Add the devices section in the following example. The defaults section in the following example sets some defaults that are generally applicable. For other specific configurations, such as excluding volumes from the multipath topology, see the manual 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 3			# To disable I/O queueing after retrying once when all paths are down
    polling_interval 5         # Set path check polling interval to 5 seconds
    find_multipaths yes        # To allow multipath to take control of only those devices that have multiple paths 
}
devices {
  device {
    vendor "MSFT"
    product "Virtual HD"
  }
}

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

Attach volumes to the client

Use the following script to create your connections. To execute it, collect or determine the following parameters:

• subscription: Subscription ID
• g: Resource Group Name
• e: Elastic SAN Name
• v: Volume Group Name
• n <vol1, vol2, ...>: Names of volumes 1 and 2 and other volume names that you might require, comma separated
• s: Number of sessions to each volume (set to 32 by default)

Copy the script from here and save it as a .py file, for example, connect.py. Then execute it with the required parameters. The following is an example of how you'd run the script:

./connect.py --subscription <subid> -g <rgname> -e <esanname> -v <vgname> -n <vol1, vol2> -s 32

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

Set session number

Use 32 sessions for each target volume to reach the maximum IOPS and throughput limits.

You can change the session count by running the script and following these instructions:

python3 connect_for_documentation.py \ 

--subscription <your-subscription-id>\ 

-g <resource-group>\ 

-e <elastic-san-name>\ 

-v <volume-group-name>\ 

-n volume1 volume2 \ 

-s <value>

Next steps

Configure Elastic SAN networking