Tianon's Ramblings ✿

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iSCSI in Debian

11 Jan 2018

I’ve recently been playing with Debian’s iSCSI support, and it’s pretty neat.

It was a little esoteric to set things up, so I figured I’d write up a quick blog post of exactly what I did both for my own future-self’s sake and for the sake of anyone else trying to do something similar.

The most “followable” guide I found was https://www.certdepot.net/rhel7-configure-iscsi-target-initiator-persistently/ (which the below is probably really similar to).

The exact details of what I was trying to accomplish are as follows:

On my-desktop, I used the targetcli-fb package to configure my iSCSI target:

$ sudo apt install targetcli-fb

$ # create the sparse file
$ mkdir -p /home/tianon/iscsi
$ truncate --size=100G /home/tianon/iscsi/my-rpi3-docker.img

$ # launch "targetcli" to configure the iSCSI bits
$ sudo targetcli

# create a "fileio" object connected to the new sparse file
/> /backstores/fileio create name=my-rpi3-docker file_or_dev=/home/tianon/iscsi/my-rpi3-docker.img

# enable "emulated TPU" (enable TRIM / UNMAP / DISCARD)
/> /backstores/fileio/my-rpi3-docker set attribute emulate_tpu=1

# create iSCSI storage object
/> /iscsi create iqn.1992-01.com.example.my-desktop:storage:my-rpi3-docker

# create "LUN" assigned to the "fileio" object
/> /iscsi/iqn.1992-01.com.example.my-desktop:storage:my-rpi3-docker/tpg1/luns create /backstores/fileio/my-rpi3-docker

# create an ACL for my-rpi3 to connect
/> /iscsi/iqn.1992-01.com.example.my-desktop:storage:my-rpi3-docker/tpg1/acls create iqn.1992-01.com.example:node:my-rpi3
# and set a CHAP username and password, for security
/> /iscsi/iqn.1992-01.com.example.my-desktop:storage:my-rpi3-docker/tpg1/acls/iqn.1992-01.com.example:node:my-rpi3 set auth userid=rpi3 password=holy-cow-this-iscsi-password-is-so-secret-nobody-will-evvvvvvvvver-guess-it

Additionally, I’ve been experimenting with firewalld on my-desktop, so I had to add the iscsi-target service to my internal zone to allow the traffic from my-rpi3.

On my-rpi3, I used the open-iscsi package to configure my iSCSI initiator:

$ sudo apt install open-iscsi

$ # update "InitiatorName" to match the value from our ACL above
$ sudo vim /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.1992-01.com.example:node:my-rpi3

$ # update "node.startup" and "node.session.auth.*" for our CHAP credentials from above
$ sudo vim /etc/iscsi/iscsid.conf
...
node.startup = automatic
...
node.session.auth.authmethod = CHAP
node.session.auth.username = rpi3
node.session.auth.password = holy-cow-this-iscsi-password-is-so-secret-nobody-will-evvvvvvvvver-guess-it
...

# restart iscsid so all that takes effect (especially the InitiatorName change)
$ sudo systemctl restart iscsid

$ sudo iscsiadm --mode discovery --type sendtargets --portal my-desktop-ip-address
$ sudo iscsiadm --mode node --targetname iqn.1992-01.com.example.my-desktop:storage:my-rpi3-docker --portal my-desktop-ip-address --login

$ lsblk --scsi
NAME HCTL       TYPE VENDOR   MODEL             REV TRAN
sda  0:0:0:0    disk LIO-ORG  my-rpi3-docker   4.0  iscsi

$ sudo fdisk /dev/sda
...
$ sudo mkfs.ext4 -T news -L my-rpi3-docker /dev/sda1
...
$ lsblk | grep my-rpi3-docker
... UUID="xxx" ...
$ sudo vim /etc/fstab
...
UUID="xxx" /var/lib/docker ext4 noatime,discard,_netdev 0 0
...
$ sudo systemctl stop docker
$ sudo mount /var/lib/docker
$ sudo systemctl start docker

$ # yay, profit (and should auto-remount properly on boot and everything, too)

(Obviously, replace iqn.1992-01.com.example with an appropriate IQN for your own domain as described on Wikipedia, and other values as appropriate like the username/password, hostnames, IPs, etc.)

As for speed, I was able to get the following result from a very simplified dd-based speed test – YMMV:

$ dd if=/dev/zero of=/var/lib/docker/testfile bs=100M count=10 oflag=direct
10+0 records in
10+0 records out
1048576000 bytes (1.0 GB, 1000 MiB) copied, 97.9608 s, 10.7 MB/s