Re: Restrictions in FCP point-to-point topology

2011-05-02 Thread Mark Post 
 On 4/28/2011 at 12:19 PM, Alan Ackermanalan.acker...@bankofamerica.com 
 wrote:

 We are planning to use FCP disk with a z/Linux under z/VM system,
 running under z/VM 5.4.  To reduce cost, we are planning to use the
 point-to-point topology.

If you don't use a SAN fabric switch, discovering and configuring LUNs on your 
Linux guests will be entirely manual, and even less fun than usual.  This is 
due to the fact that a number of things the discovery tools depend upon are 
provided by the switch itself.

I know of a couple of customers that went with point-to-point.  It made their 
life (and that of their IBM business partner and our TSS) miserable.


Mark Post

Restrictions in FCP point-to-point topology

2011-04-28 Thread Alan Ackerman 
Restrictions in FCP point-to-point topology

We are planning to use FCP disk with a z/Linux under z/VM system,
running under z/VM 5.4.  To reduce cost, we are planning to use the
point-to-point topology.

Are there any restriction in using this topology?

I seem to remember some restrictions mentioned in the presentation given
at SHARE when the point-to-point support first appeared in z/VM.

The load (write) volume will be high (the higher the better), but only
occasionally and for less than a day at a time.  Another reason to use
point-to-point is that we think it will perform better without the
switch.

We want to have a 4TB LVM, spread across 8 LUNs.

Picture:

+---++---+
|  LPAR 1   ||  LPAR 2   |
|   +---+|   +---+
|   |  z/VM 1   |-FCP--4TB---FCP-|   |  z/VM 2   |
|   |   +---+  disk  |   |   +---+
|   |   |  Linux 1  ||   |   |  Linux 2  |
+---+---+---++---+---+---+

A wider picture is

z/OS--Hipersocket--Linux--FCP--Hipersocket--z/OS
DB2  disk

I found a presentation Introduction to SCSI over FCP for Linux on
System z at http://www.vm.ibm.com/education/lvc/lvc1020c.pdf.  It
mentions (on foil 6) the two topologies, point-to-point and switched
fabric, but gives no restrictions.

Thanks!

Alan Ackerman
Alan (dot) Ackerman (at) Bank of America (dot) com