Zoning is not physical separation

I see this comment occasionally and it makes me bristle:

“Disk and tape traffic must be in separate zones because they have different characteristics. If they are in the same zone this can cause performance problems or have other adverse affects.”

True statement or totally wrong?

Well actually kinda wrong…  If you have a single HBA with only one port, then separating disk and tape traffic into separate zones does NOTHING to get around the fact that both streams of traffic (random bursty disk traffic and sequential streaming tape traffic) are all coming from or going to the same HBA port.    All zoning achieves in this case is stop the disk and tape devices from talking to each other (something that in general they are not interested in doing).

Separating disk and tape traffic is best done with separate HBA ports (whether thats a dual ported HBA or two single port HBAs).

So lets change the wording:

“Disk and tape traffic should ideally be handled by separate HBA ports, because they have different characteristics. If both traffic types use the same HBA port this can cause performance problems or have other adverse affects.”

Guess what?   This advice has not changed since 2001.


About Anthony Vandewerdt

I am an IT Professional who lives and works in Melbourne Australia. This blog is totally my own work. It does not represent the views of any corporation. Constructive and useful comments are very very welcome.
This entry was posted in IBM Storage and tagged , , , , . Bookmark the permalink.

6 Responses to Zoning is not physical separation

  1. Dennis Skinner says:

    I don’t think I’ve ever heard this conversation without mention of separate HBA’s, so I guess that is a good thing.

    I do have a related question that I was planning on asking our Sales Engineer, but why not ask here too…. What about VTL (specifically ProtecTier)? I’d expect the perf characteristics to look like tape to the SAN, but it is Disk. What is the official recommendation? Do you send the VTL traffic to the Disk HBA, the Tape HBA, or does it get its own category and I need to plan to have 3 sets of HBA’s in my backup host?

    • avandewerdt says:

      Its a great question. The recommendation to separate traffic is a catch all statement to protect clients from implementing a solution that may not work well in the long run. If non-complementary traffic is hitting the same HBA, diagnosing the issue can be problematic and asking a client to try separate HBAs is not as easy as it sounds after the solution has been implemented.

      So what to do virtual tape? Its the same style traffic sent to a virtual device. The TS7650 Redbook says: For best performance and reliability, use separate HBA ports on the media server to
      connect to 3958-DD4 or 3958-AP1 servers only. If this is not possible, establish zones where ProtecTIER system ports only see media server HBA ports and not other tape

  2. Cris says:

    Hrmm. While I’ll agree that disks and tape should be mapped to different HBA ports for best performance. I disagree that zoning does nothing. Yes, there is still a mixture of workloads, but this is no different than if you have two or more targets attached (storage or otherwise) that have different workload profiles. Zoning has more significants from a protocol perspective rather than from a practical one. The whole point of zoning is to limit RSCN broadcasts, not to segregate workloads.

    But thats just my 2 cents

  3. Ed says:

    Hi, Anthony. On a multi-ported FC HBA, do the HBA settings apply to all the FC ports on the HBA? If so, seems like we’d have to dedicate HBAs to disk or tape??? Thanks!

    • The good news is that a multi-port HBA is effectively like two HBAs on one card, so each have independent settings.
      This makes a dual port HBA like a QLA2462 a great choice as it is like buying two cards but using only one slot.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s