SAN Zoning - best practices ?

Hi,

I'm rather a newbie in SAN environment and I'm asking a lot of
questions about zoning considerations. Here is our SAN :

5 Windows 2003
2 Windows 2000
1 Aix
1 storage disks area
1 robot library
2 SAN switchs (sphereon 4300)


All servers and storage devices have 2 HBA, each one connected to one
of the 2 switchs. The switchs are not connected together (no fabric
mode).

I've currently 2 zones : one for disk access and one for robot access.
In the first, there are all the servers + disks, in the second one,
there are all the servers + robot.

Most of the time, all is ok, I've no problem with this configuration.
But, when I connect new servers, or when I modify zoning
configuration, it happens that one server losts his connection with
the san device... I wonder if my zoning configuration is good ?

What would you do with this kind of SAN :
one zone by OS type ?
one zone by server ?
only one zone ?

Thanks in advance for your help.

I'm not sure what other SAN vendors say about zoning practices, but
EMC's policy is that one-to-one zoning is preferred. In other words,
each zone should contain exactly one initiator (host), and one
target(disk array port/tape drive/robot).
That being said, I don't think changing the zone should disrupt a
single host. It is more likely that your HBA is not properly
configured to support (or does not support) fabric mode. I have had
similiar issues using Emulex 2200a adapters. They are suppose to only
support Arbitrated-loop; however, they work fine until a zoning/masking
change-- then they freak out.

More on one-to-one zoning:

I practice one-to-one zoning on all my SAN switches, and even name my
zones according to the nodes within them, since not all my switches
support WWN nicknames as well as I'd like. i.e.
hostname_hba0_symm_0000_fa12b.

One-to-one zoning's advantages include:
1.) Limit the exposure to risk during changes-- if you accidentally
remove a storage port from a zone with 15 hosts, you could effect all
of those hosts.
2.) Reduce complexity by allowing the administrator to immediately see
the members of a zone based on its name.
3.) Some switches support RSCNs to just zone members

Possible disadvantages are that you may have to modify multiple zones
when changing out initiators/targets... other than that I can think of
any, though I'm happy to hear others' opinions...

HTH
Aaron