Re: FreeBSD iscsi target

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