Nicholas A. Bellinger, on 04/14/2010 12:45 AM wrote:
On Tue, 2010-04-13 at 23:23 +0400, Vladislav Bolkhovitin wrote:
Nicholas A. Bellinger, on 04/13/2010 10:37 PM wrote:
On Tue, 2010-04-13 at 21:09 +0400, Vladislav Bolkhovitin wrote:
LIO doesn't support 1 to many pass-through devices sharing, so SCST in
the only option.
Sorry, but this statement about your perceived limitiations wrt TCM/LIO
is completely incorrect.
Using a single passthrough backstore device (eg: plain /dev/sdX) with
TCM/pSCSI (or any TCM subsystem plugin) has been supported since the
dawn of time to allow for any number of TCM_Loop Virtual SAS Ports with
SG_IO going into KVM Guest. The same is also true for LIO-Target
(iSCSI) and TCM_FC (FCoE) ports as well regardless of TCM subsystem
backstore.
Perhaps you would be so kind to provide a TCM/LIO source code reference
from where you came up with this make-believe notion..?
I've just rechecked with the latest
git://git.kernel.org/pub/scm/linux/kernel/git/nab/lio-core-2.6.git and
still wasn't able to find in LIO required pieces of functionality to
support 1 to many pass-through. I see only code for non-enforced 1 to 1
pass-through (single initiator only). You can use with it more
initiators only as the SCSI violation, from pointing on which I started
my participation in this discussion.
Sorry, but listing the path to my git tree on k.o is not the same as
citing a actual TCM/LIO source+line reference.
That's interesting. How can I point to the code which doesn't exist?
Particularly, I can't see the code, which in pass-through mode upon
receive of RESERVE command sends it also to the backend device, if
necessary (i.e. only the first time), and then sends RELEASE command to
the device upon the reservation holder removal. Could you point me on
the *exact* code which implements that?
Again, since *you* are the one making a claim, *you* are the one
expected to back it up with a concrete code reference and example
scenario. Please, do the leg-work yourself wrt TCM SPC-3 persisetent
reservations and legacy SPC-2 reservations instead of expecting me to do
the actual work for you to verify your own fanciful claims about target
mode, seriously..
So, short of you being able to produce a response that is concrete and
human-readable, your claim will once again be dismissed as generic
hand-waving.
Well, this is an Open Source and in Open Source code auditing is the
most important way to verify an implementation. I reviewed TCM/LIO and
my conclusion is pretty clear: it misses too many important bits to be a
1 to many pass-through implementation, so it implements only
not-enforced 1 to 1 pass-through. You implemented reservations
emulation, but that's _NOT_ enough. I gave an example of the one among
many missed functionality.
I'm not going to go any deeper than I've already gone doing your home
work for you and explaining you the SCSI basics (although for me it's
really hard to believe that a person implemented something as big as
TCM/LIO can't see such obvious things), because when I did it before,
when you asserted that if a pass-trough device supports Persistent
Reservations, LIO in pass-through mode with this device automatically
supports them too, which is obviously wrong (see the end of
http://lkml.org/lkml/2008/7/14/273), I didn't have even a bit of
appreciation for my effort. Instead I received privately from you
insulting and threatening e-mails.
If you are not agree with my conclusion about pass-through
implementation in TCM/LIO, you can either point us on the code
implementing the necessary functionality, which I missed, or argue why
it isn't needed. But if you continue attacking me personally trying to
discredit me, everybody will see that my conclusions are definitely
correct as well as which is your preferred way of cooperation.
Vlad
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