iSCSI basic concepts

Question

I have just detected that in one of my hosts (this is a virtual machine run by a cloud provider) there is a process eating up some bandwidth:

NetHogs version 0.6.0

  PID USER     PROGRAM                      DEV        SENT      RECEIVED       
4617  root     iscsid                       eth0     170.808       7.957 KB/sec
13300 root     sshd: user1   [priv]         eth0       0.000       0.841 KB/sec
26042 nagios   ssh                          eth0       0.745       0.789 KB/sec

  TOTAL                                              171.656      10.287 KB/sec 

I have googled a bit about this iscsid process (new thing to me), and it seems this is a kind of "SCSI over TCP" daemon. Fine with that. I have some questions:

1. Why is this process using bandwidth continuously?
2. I would like to know what is being mounted using the iSCSI protocol.
3. What tools are there to get information about iSCSI configuration, mount points, ...
4. Is the whole disk "mounted" via iSCSI, or just a partition, or what?
5. Do I have a "disk" in my VM? The way I have myself setup virtual machines (with XEN) has always been using .qcow2 files in the host filesystem.
6. If there is no disk, how is the VM booting?

Mount offers no clues about it.

mount

/dev/sda1 on / type ext3 (rw,noatime,nodiratime,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
/sys on /sys type sysfs (rw,noexec,nosuid,nodev)
varrun on /var/run type tmpfs (rw,noexec,nosuid,nodev,mode=0755)
varlock on /var/lock type tmpfs (rw,noexec,nosuid,nodev,mode=1777)
udev on /dev type tmpfs (rw,mode=0755)
devshm on /dev/shm type tmpfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
/dev/sda2 on /home type ext3 (rw,noatime,nodiratime)

UPDATE

$ sudo iscsiadm -m session -P 0
tcp: [1] 91.131.224.20:3260,1 iqn.2017-11.net.ovh:r44247vol0

$ sudo fdisk -l

Disk /dev/uba: 4002 MB, 4002910208 bytes
32 heads, 63 sectors/track, 3878 cylinders
Units = cylinders of 2016 * 512 = 1032192 bytes
Disk identifier: 0x20fb6d2b

   Device Boot      Start         End      Blocks   Id  System
/dev/uba1   *           1        3878     3908992+   b  W95 FAT32

Disk /dev/sda: 21.4 GB, 21474836480 bytes
64 heads, 32 sectors/track, 20480 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Disk identifier: 0x00003fd3

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           3        5002     5118976+  83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2            5002       20001    15358976   83  Linux
Partition 2 does not end on cylinder boundary.

$ sudo dmesg | grep -A10 "iSCSI Init"
(no output)

The output fdisk command is quite obscure to me: does this mean it is iSCSI related? I do not see any reference to iSCSI there ...

Answer 1

1. Something is connected to it and requesting data continuously.
2. Depends on what software you're running
3. See #2.
4. Could be, iSCSI provides block storage, which can be backed by disk, partition, files, in a thin or fat manor.
5. Most VMs have virtual disks they boot off, but it's not required, and we'd have no idea how you setup yours.
6. VMs can boot by all the same mechanisms as physical computers (PXE, iSCSI, FC, IB, Floppy, USB drive, etc).

Answer 2

What is the output of fdisk -l and dmesg | grep -A10 "iSCSI Init"?

That will show if any block devices are mapped or were discovered.

Also, iscsiadm -m session -P 0 will show the full iSCSI session status output.