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RE: An area for operations growth - Storage Area Nets in MANS

  • From: Gordon Cook
  • Date: Fri May 16 19:29:11 2003

Sorry for any confusion. Fiber channel is old tech for sure and there was no implied intent to evaluate the tech itself. Roxane has apparently observed that on devices like the core directors the number of fiber channel ports being ordered is going up dramatically.... apparently about the only thing it makes sense to do with such ports is to use them for SANs. The remark was not intended to be definitive or in great depth and was added almost as an after thought at the end of a short (35 minute) interview at the san jose airport.

Certainly there is major movement in large fiber based in metropolitan areas that have been built and are being built by banks, and fortune 500 kinds of enterprises as they move a LOT of data and voice traffic off the PSTN and on to new cheap equipment that they can get a much better return for on the dollars they invest. All a part of the commoditization and decentralization of telecom.

I am not an expert in the application of the technology being discussed. However at some time in the next six month i probably will want to explore this in much more depth.

 Although these new real time applica tions will clearly send more
 data over the network, the real killer application is going to be
 remote storage and synchronous storage.  Synchronous storage means
 that you have two large servers doing the exact same thing at the
 exact same time in two different locations.

 COOK Report:  Like a decentralized disk array?

 Googin:  Yes.  The backbone has to be incredibly fast because you
 cannot complete a transaction until you have acknowledgments from
 both disk drives.  This will happen.  Probably this year.  What they
 are already doing is taking fiber channel and putting that on a
 Cienna Core Director optical switch port.  Half of the ports being
 sold on the Core Director now are fiber channel.  They aren't even
 Ethernet.  And this is used for storage area nets (SANs).  These are
 corporate MANs and will have nothing to do with sales to service
 providers.  They are bypass business services where the storage
 arrays may not be more than a kilometer or two apart.  These SANs are
 backing up continuously terabytes of data.  We are talking huge
 applications that will use every bit of access to every bit of
 capacity they can get.

Erm - perhaps I'm misunderstanding what Googin is trying to say here,
but if he's talking about synchronous remote replication over fibre
channel, this exists today. In fact, it has existed for years, and
before it was over fibre channel, it was over ESCON. Today, still, if
you want to go father than a certain distance (70km maybe?) its
generally recommended to switch over to ESCON rather than fibre channel.

In practicality, complete remote replication is often inadvisable for
high-performance, heavy-write applications. The rule of thumb is that
every KM adds another millisecond worth of I/O transaction time, so a
few kilometers distance can add a significant overhead to writes.
Not to mention Fibre Channel is very unkind when it comes to recovery
from fabric segmentation. A poorly designed (or just very unlucky) SAN
can be completely downed on both sides of the split, somewhat ruining
the disaster recovery strategy if the production and DR storage networks
are both taken down.
Ugh - I'll be very happy when fibre channel is dead and buried.

Matthew Zito
GridApp Systems
Email: [email protected]
Cell: 646-220-3551
Phone: 212-358-8211 x 359

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