North American Network Operators Group

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

  • From: Matthew Zito
  • Date: Fri May 16 18:25:42 2003

> 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