iSCSI provides block-level access to storage devices by carrying SCSI commands over a TCP/IP network. A NAS, like one from Synology, can act as an iSCSI remote storage device.
The Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical, and logical interfaces. SCSI-1 was published in 1986!
There are two parties in an iSCSI setup… the client and the server.
- The client is called the Initiator
- The server, the remote storage, is the Target
Many NAS devices support iSCSI. This is how you do it on a Synology NAS running DSM 7.
Note: If you setup iSCSI and have active connections to the Target, your NAS won't power down for any scheduled shutdowns you may have in your Power Schedule.
- Open the DSM webpage and loging.
- Open Package Center
- Search for SAN
- Install the "SAN Manager" if it isn't already installed.
- Open the SAN Manager
- Click on iSCSI
- Click Add (Note: If you already have an iSCSI Target, click Create)
- Use the default values and click Next
- Pick "Create a new LUN" and click Next
- Enter the size you want (in GB) and click Next
- Click Done.
Note the IQN, it will be something like iqn.2000-01.com.synology:MYNAS.Target-1.73d9a1ba16c, you will need it when you edit /etc/iscsi/initiatorname.iscsi.
It is important to always use sudo when running these iSCSI commands. Some of the commands will work without sudo but the records, status, and database of current connections
is stored on a per-user basis, so when you switch between root and pi the results are different.
Install open-iscsi.
sudo apt update
sudo apt -y install open-iscsi
The iSCSI qualified name (IQN) of the Pi is defined in /etc/iscsi/initiatorname.iscsi. During installation the initial IQN will be generated automatically. If you wish to create a new IQN then use the iscsi-iname utility, it will print out a new IQN for you.
Now we need to change some of the Open-iSCSI default configuration.
sudo nano /etc/iscsi/iscsid.conf
Find the "Startup settings" section and comment out node.startup = manual and uncomment node.startup = automatic
#*****************
# Startup settings
#*****************
# To request that the iscsi initd scripts startup a session set to "automatic".
node.startup = automatic
#
# To manually startup the session set to "manual". The default is manual.
#node.startup = manual
If you set and username and password for the Target then go to the "CHAP Settings" section and set a CHAP username and password for initiator
# *************
# CHAP Settings
# *************
# To enable CHAP authentication set node.session.auth.authmethod
# to CHAP. The default is None.
node.session.auth.authmethod = CHAP
# To set a CHAP username and password for initiator
# authentication by the target(s), uncomment the following lines:
node.session.auth.username = gary
node.session.auth.password = not12345678
Restart iSCSI services.
sudo systemctl restart iscsid open-iscsi
sudo iscsiadm -m discovery -t sendtargets -p 192.168.1.104
Where 192.168.1.104 is the IP address of your NAS.
Confirm results of discovery
sudo iscsiadm -m node -o show
Login to the Target
sudo iscsiadm -m node --login
This should be done even if you aren't using authentication
Confirm the established session with the Target
sudo iscsiadm -m session -o show
The remote iSCSI device should now appear as a block device on the Pi. You should see sda now as a device. Use the following commands to check the status of sda
dmesg | grep scsi
dmesg | grep "\[sd"
cat /proc/partitions
/proc/partitions should like something like this:
major minor #blocks name
1 0 4096 ram0
1 1 4096 ram1
1 2 4096 ram2
1 3 4096 ram3
1 4 4096 ram4
1 5 4096 ram5
1 6 4096 ram6
1 7 4096 ram7
1 8 4096 ram8
1 9 4096 ram9
1 10 4096 ram10
1 11 4096 ram11
1 12 4096 ram12
1 13 4096 ram13
1 14 4096 ram14
1 15 4096 ram15
179 0 62367744 mmcblk0
179 1 1580296 mmcblk0p1
179 2 1 mmcblk0p2
179 5 32767 mmcblk0p5
179 6 262143 mmcblk0p6
179 7 60475392 mmcblk0p7
8 0 134217728 sda
Now that there is a block device (i.e. sda) on your Pi, it can be partitioned and formatted like any other HDD/SSD.
You might find this video useful: How to Partition and Format a Disk in Linux
Assuming that the iSCSI Target is seen as /dev/sda by your Raspberry Pi:
sudo fdisk /dev/sda
Use g to create a new empty GPT partition table
Command (m for help): g
Created a new GPT disklabel (GUID: 5C8EB2FC-E8AC-4B45-878A-F3D7431D1463).
The old dos signature will be removed by a write command.
Use n to create a new partition:
Command (m for help): n
Partition number (1-128, default 1):
First sector (2048-268435422, default 2048):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-268435422, default 268435422):
Created a new partition 1 of type 'Linux filesystem' and of size 128 GiB.
Use w to write the new partition table to the disk and exit.
sudo mkfs.ext4 /dev/sda1
The remote iSCSI drive can only be mounted after boot-up has been completed. This means the networking is up and open-iscsi is running.
sudo nano /etc/mount_iscsi.sh
Add these lines:
#!/bin/sh
sleep 60
mount /dev/sda1 /iscsimnt
Where /iscsimnt is the mount point you want to use. Make sure you do a sudo mkdir -p /iscsimnt to create the mount point.
Give the file execute permission:
sudo chmod +x /etc/mount_iscsi.sh
Now edit /etc/rc.local and add a line to call the new script. rc.local is executed at the end of each multiuser runlevel.
sudo nano /etc/rc.local
Add this line near the bottom, but before exit 0
sudo /etc/mount_iscsi.sh &
It should be possible to mount the iSCSI drive via the /etc/fstab file. According to this comment under my video https://www.youtube.com/watch?v=80HgEhlq_pA&lc=UgwCAwXe7tRfYQkl7LV4AaABAg you need to add "_netdev,x-systemd.requires=iscsi.service" to the mount options.
Restart your Pi. Wait a few seconds after the full boot has completed and then check that the iSCSI Target is mounted on /iscsimnt
You can disconnect (logout) of a Target with:
sudo iscsiadm -m node --logout
To delete the whole discovery database use:
sudo iscsiadm -m node -o delete