Re: FreeBSD iscsi target

On Thu, Jul 3, 2014 at 10:13 AM, Slawa Olhovchenkov <slw_at_zxy.spb.ru> wrote:
> On Thu, Jul 03, 2014 at 09:31:45AM +0100, Nikolay Denev wrote:
>
>> On Thu, Jul 3, 2014 at 12:06 AM, Kevin Oberman <rkoberman_at_gmail.com> wrote:
>> > On Wed, Jul 2, 2014 at 1:36 PM, Slawa Olhovchenkov <slw_at_zxy.spb.ru> wrote:
>> >
>> >> On Wed, Jul 02, 2014 at 12:51:59PM -0700, Kevin Oberman wrote:
>> >>
>> >> > On Wed, Jul 2, 2014 at 4:26 AM, Slawa Olhovchenkov <slw_at_zxy.spb.ru>
>> >> wrote:
>> >> >
>> >> > > On Tue, Jul 01, 2014 at 10:43:08PM -0700, Kevin Oberman wrote:
>> >> > >
>> >> > > > On Tue, Jul 1, 2014 at 4:13 PM, Slawa Olhovchenkov <slw_at_zxy.spb.ru>
>> >> > > wrote:
>> >> > > >
>> >> > > > > On Tue, Jul 01, 2014 at 11:12:52AM +0200, Edward Tomasz Napierala
>> >> > > wrote:
>> >> > > > >
>> >> > > > > > Hi.  I've replied in private, but just for the record:
>> >> > > > > >
>> >> > > > > > On 0627T0927, Sreenivasa Honnur wrote:
>> >> > > > > > > Does freebsd iscsi target supports:
>> >> > > > > > > 1. ACL (access control lists)
>> >> > > > > >
>> >> > > > > > In 10-STABLE there is a way to control access based on initiator
>> >> > > > > > name and IP address.
>> >> > > > > >
>> >> > > > > > > 2. iSNS
>> >> > > > > >
>> >> > > > > > No; it's one of the iSCSI features that seem to only be used
>> >> > > > > > for marketing purposes :-)
>> >> > > > > >
>> >> > > > > > > 3. Multiple connections per session
>> >> > > > > >
>> >> > > > > > No; see above.
>> >> > > > >
>> >> > > > > I think this is help for 40G links.
>> >> > > > >
>> >> > > >
>> >> > > > I assume that you are looking at transfer of large amounts of data
>> >> over
>> >> > > 40G
>> >> > > > links. Assuming that tis is the case, yes, multiple connections per
>> >> > > session
>> >> > >
>> >> > > Yes, this case. As I know, single transfer over 40G link limited by
>> >> > > 10G.
>> >> > >
>> >> > ??? No, not at all. Getting 40G performance over TCP is not easy, but
>> >> there
>> >> > is no 10G limitation.
>> >>
>> >> As I know (may be wrong) 40G is bundled 4x10G link.
>> >> For prevent packet reordering (when run over diferrent link) all
>> >> packets from one sessoin must be routed to same link.
>> >> Same issuse for Etherchannel.
>> >>
>> >
>> > No, 40G Ethernet is  single channel from the interface perspective.. What
>> > my be confusing you is that they may use "lanes" which, for 40G,  are
>> > 10.3125G. But, unlike the case with Etherchannel, these lanes are "hidden"
>> > from the MAC. The interface deals with a single stream and parcels it out
>> > over the 10G (or 25G) lanes. All 100G optical links use multiple lanes
>> > (4x25G or 10x10G), but 40G my use either a single 40G lane for distances of
>> > up to 2km or 4x10G for longer runs.
>> >
>> > Since, in most cases, 40G is used within a data center or to connect to
>> > wave gear for DWDM transmission over very long distances, most runs are
>> > under 2km, so a single 40G lane may be used. When 4 lanes are used, a
>> > ribbon cable is required to assure that all optical or copper paths are
>> > exactly the same length. Since the PMD is designed to know about and use
>> > these lanes for a single channel, the issue of packet re-ordering is not
>> > present and the protocol layers above the physical are unaware of how many
>> > lanes are used.
>> >
>> > Wikipedia has a fairly good discussion under the unfortunate title of 100
>> > Gigabit Ethernet <https://en.wikipedia.org/wiki/100_Gigabit_Ethernet>.
>> > Regardless of the title, the article covers both 40 and 100 Gigabit
>> > specifications as both were specified on the same standard, 802.3ba.
>> >
>> > --
>> > R. Kevin Oberman, Network Engineer, Retired
>> > E-mail: rkoberman_at_gmail.com
>> > _______________________________________________
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>>
>> I found this white paper useful in understanding how this works :
>> http://www.cisco.com/c/en/us/products/collateral/switches/nexus-3000-series-switches/white_paper_c11-726674.pdf
>
> In real world "Reality is quite different than it actually is".
> http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-6500-series-switches/white_paper_c11-696669.html
>
> See "Packet Path Theory of Operation. Ingress Mode".
>

Interesting, however this seems like implementation specific detail,
and not limitation of native 40Gbit ethernet.
Still, it's something that one must be aware of (esp when dealing with
Cisco gear :) )

I wonder why they are not doing something like this :
http://blog.ipspace.net/2011/04/brocade-vcs-fabric-has-almost-perfect.html

--Nikolay