[Bug 1034015] Re: Fails to connect to iSCSI target

[Peter Petrakis]

@roysk

The thing about inquiry data is that it's incumbent on the target to provide
what the initiator has asked of it. What is open-iscsi connecting to, another SAN,
if so which make and model? If it's not a HW SAN could you setup an software 
iSCSI target server and  connect with the existing open-iscsi tool set to see
if the short inquiry phenomenon follows the SAN or the the client?

In my experience, these sort of faults usually are the result of a SCSI target
that's not quite ready. Sure it may be fully provisioned, but if the SAN is busy
serving other requests, *it's operating system* can starve out the target and
cause unpredictable results.  It's an equal opportunity offender, affecting
software iSCSI targets and inefficient HW SAN firmware (also software :).

Getting 36 bytes of inquiry data is trivial, something is really wrong if we can't
get even that from the target.

https://en.wikipedia.org/wiki/SCSI_Inquiry_Command

If you are using a software target to begin with, consider adding cgroups to
ensure it has a minimum of CPU time to perform it's tasks in a timely manner;
or simply decreasing the net workload on the system and see if that improves
reliability.

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https://bugs.launchpad.net/bugs/1034015

Title:
  Fails to connect to iSCSI target

Status in “linux” package in Ubuntu:
  Triaged
Status in “open-iscsi” package in Ubuntu:
  Incomplete

Bug description:
  Connecting from an Ubuntu 12.04LTS server to a SANRAD switch offering
  iSCSI connectivity, fails. First, look for targets

  root at media2:~# iscsiadm -m discovery -t st -p 172.31.1.15
  172.31.1.15:3260,65535 bigmedia1
  172.31.1.14:3260,65535 bigmedia1
  172.31.1.16:3260,65535 bigmedia1
  172.31.1.15:3260,65535 media1target
  172.31.1.14:3260,65535 media1target
  172.31.1.16:3260,65535 media1target
  172.31.1.15:3260,65535 bigmedia2
  172.31.1.14:3260,65535 bigmedia2
  172.31.1.16:3260,65535 bigmedia2

  Lots of nice targets - now connect to one

  root at media2:~# iscsiadm -m node -T bigmedia1 -p 172.31.1.15 -l
  Logging in to [iface: default, target: bigmedia1, portal: 172.31.1.15,3260]
  Login to [iface: default, target: bigmedia1, portal: 172.31.1.15,3260]: successful
  root at media2:~# echo $?
  0

  Apparently connected - it says successful, and returns zero. Now,
  check partitions

  root at media2:~# cat /proc/partitions
  major minor  #blocks  name

    11        0    1048575 sr0
     8        0  731445248 sda
     8        1    1048576 sda1
     8        2  730395648 sda2
   252        0   20971520 dm-0
   252        1    8388608 dm-1

  Nothing new - sda is my root drive, the new one should be in there as
  sdb. Checking dmesg, it has two new lines

  [  358.391438] scsi6 : iSCSI Initiator over TCP/IP
  [  358.645490] scsi scan: INQUIRY result too short (5), using 36

  Please see http://karlsbakk.net/tmp/iscsi-debug.txt for a login
  attempt with -d 200 and http://karlsbakk.net/tmp/iscsi-fail.pcap for a
  traffic dump between the two machines during login attempt.

  Please note that with open-iscsi on a CentOS 5.8 machine of the same
  make, this works perfectly.

  roy

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