SAN Design Question

[estech25]

I have found myself between two design alternatives and am wondering which is the safer/ technically correct path to take.
I need a SAN starting with 75 host ports which must be expandable to a maximum of 200 host ports. I am wondering whether to use one large director switch (FOr example one with 256 ports) or go for a Core/Edge design which might incorporate many many switches and provide the necessary ports. Is there anything essentially wrong with using a standalone director switch for a large SAN? Is there any technical advantage to either method?

 

[Chacalinc]

I recommend to use 2 x 128ports director. So you have a very good performance (given by directors) and high availability.

Cheers.

Chacal, Inc.

 

[estech25]

Thanks for your response. Using two 128-port switches is fine, now is there any reason to go for the Core-Edge design using many switches? Why is that approach even mentioned in design books? (eg by Brocade)

 

[p5wizard]

now is there any reason to go for the Core-Edge design using many switches?

One reason I see: It is easier (cheaper) to put an edge switch in a remote location using a few longwave links to the core switches, than to longwave link all the servers from that remote location to a central switch or director.


HTH,

p5wizard

 

[Chacalinc]

In addition to p5wizard is the maintenance... with several switches you need to:

- have several contract maintenance
- have upgrade too much switches
- have all switches with compatible firmwares
- have clear the topology for future modifications and scalability.

Cheers.

Chacal, Inc.

 

[comtec17]

A core to edge topology was orginally put in place for the reasons stated above but was intended to use to place storage/tape on Core Devices/Directors and then ISL out to the Edge using departmental switches consisting of hosts and possibly tape devices. This was also due to the amount of ports available on these devices as the edge devices were really no larger than 16 ports and Cores were between 32 and 64 ports.

In todays SAN world, there is still Core to Edge designs, but as Chacalinc stated, a mirrored fabric using directors is the "Ultimate" solution based on availability of 99.999% or 5 minutes or less of annual downtime. and a smaller footprint. This solution will also let you upgrade 1 side at a time so you will always have 1 link remaining in case of failure. And for one last note, by using "Mirrored Fabrics" (no ISL's) you keep all Fabric State Change Notifications or Registered State Change Notifications segmented to thier own fabric and will not face the risk of a single zoning change to decommision you.

If you are not in need of a five 9 architecture and you are not worried about downtime, and are ok with placing everything in 1 location, then using switches like the Cisco 9216 which is expandable to 48 ports and soon 64 ports using a 16 port blade for core and a 32/48 port blade for edge and mirroring the fabrics will also work.

 

[Breslau]

one drawback to mirrored directors is device portability. especially if your storage device, usually tape, does not support dual attachment. in that case, where the devive goes, so must the HBA talking to it. you could potentially end up with one side port starved. in a multi switched fabric, you can attach where there are open ports.

in the end tho, both approaches have +'s and -'s, just depends on what yer doing.

 

[ortica104]

Hi b,
Try to use Brightstor SAN DESIGNER , this software help You to design Your SAN .