Fabric Zoning, what’s best?

How to properly zone a Fabric is a recurrent topic in the storage world, there are different kinds of zoning starting from the most permissive (multiple-initiators, multiple-targets) to the most segmented (single-initiator, single-target) but before the deep dive, let’s explain the basics:

There are three types of zoning:

• Hard Zoning
• Soft Zoning
• Mixed Zoning

Hard Zoning is when your zones are made using Port numbers instead of WWNs, It is quite useful if you’re zoning the switch in advance, so if you do not know the WWNs yet you can label the ports and instruct the field technician to just plug the right connectors in the right ports, it is also useful to reduce the number of zones when you use N-Port virtualization (NPIV) where multiple N-Ports (Node Ports) are presented to a single physical Port.

Soft Zoning instead is a zoning made with WWNs instead of physical ports, it’s currently the preferred type of zoning by most people in the industry, It is the most granular type of zoning, and the one we will cover here in this post.

There’s also Mixed Zoning, discouraged by everyone, and it consist of a zone with a mix of Ports and WWNs, it’s currently the worst choice because normally the ASICs of the switch cannot segment the traffic this way and they need to resort using the switch main CPU, resulting in very bad performances.

What’s the best zoning?

Considering that historically an Initiator (Server HBA) and a Target (Storage Port) always presented themselves as such, the best zoning policy, to achieve a balance between security and manageability, was the Single-Initiator, Multiple-Targets that consist in a zoning strategy made by zones constructed with a single Initiator (Server HBA) and multiple Targets (Storage Ports), the Target ports would not talk to each other and having a single Initiator in the zone will prevent RSCN issued to other Initiators causing troubles.

But today a good number of next generation storages, present their ports as Targets and Initiators, both at the same time, so it is very important to shift to a Single-Initiator, Single-Target zoning, take a look at this:

That’s really important, especially when using array-based replication, because storage ports who have this “double personality” can see each other using normal Single-Initiator Multiple-Targets zones and you can easily break the link between the two if you don’t pay enough attention when you rezone your SAN.
Feedbacks and Comments are very welcome!

What does a Block-Level Tiered Volume look like?

So, here we go, here’s my first english language post, please be nice and don’t throw me stuff for my bad english.

Last week I had a discussion with Dimitris Krekoukias on storage performance estimation and we ended up discussing Compellent technology in great detail. We talked a lot and I’ve been very verbose on the topic but I didn’t include a single image showing how actually a volume is represented in the Compellent Storage Center array so here we go, here’s a shot from a customer of mine who’s the first Italian Compellent customer (first deployed in 2008):

As you can see the statistics shows where the data for this Volume (or LUN) is located, the “Replay” space is the Snapshot space used, the “Active” space is the changed data since the last snapshot taken (this screenshot was taken a couple of minutes after the latest snapshot).

Feel free to comment and ask question about that!.

Fabio