iSCSI¶

iSCSI (Internet Small Computer System Interface) is a protocol that allows SCSI commands to be transmitted over TCP/IP networks. It enables the creation of Storage Area Networks (SANs) using existing network infrastructure.

Key Components¶

iSCSI Initiator: The client-side component that initiates the connection to the iSCSI target.

iSCSI Target: The server-side component that provides storage resources.

How It Works¶

Initiation: The iSCSI initiator sends SCSI commands encapsulated in IP packets to the iSCSI target.

Transmission: The iSCSI target receives the IP packets, extracts the SCSI commands, and processes them.

Data Transfer: Data is transferred between the initiator and target as if it were a local storage device, even though it's over a network.

Helpful iSCSI Related Commands¶

The following are commands that are related to managing iSCSI.

List Active Sessions¶

Use the list session command to show active iscsi connections.

iscsiadm -m session

Logout of a Session¶

iscsiadm -m node --logout -T IQN

Substitute IQN shown above with actual IQN identifier.

Delete a Target¶

Make sure to logout of the session connected to the target to be deleted.

iscsiadm -m node -o delete -T IQN

Substitute IQN shown above with actual IQN identifier.

Disable iSCSI services¶

sudo systemctl enable open-iscsi
sudo systemctl enable iscsid

Troubleshooting¶

Initiator Reported Error (15 - session exists)¶

If the following error is thrown while trying to perform a backup using the iscsi device,

iscsiadm: Could not login to [iface: default, target: iqn. 2000-01.com.synology:synology-0.Target-1.76fd697e949, portal: fe80::211:32ff:fe8a:51d9,3260].
iscsiadm: initiator reported error (15 - session exists)
iscsiadm: Could not log into all portals

Connect to the PVE host that is having this issue and perfom the following command as root:

iscsiadm -m node --logoutall=all

This typically happens if the Synology server that is hosting the iscsi block device boots after the PVE servers.