Contributor
Contributor

Active vs Passive vs ALUA Storage

I'm becoming familiar with the terms active-active, active-passive, and ALUA. But I'm not sure entirely understand why one storage system is better than the other. It seems active-active would be sufficent in almost any situation. Can anyone give me an quick explanation of why one is ideally better than the other, or perhaps provide some documentation?

10 Replies
Immortal
Immortal

ALUA has to do with paths, it can be either on active passive or active active.

http://www.yellow-bricks.com/2009/09/29/whats-that-alua-exactly/

Active - Active means that a typical SAN has 2 nodes (or more).  each node is participating in taking requests from servers for access to storage.  So in this way the traffic is load balanced across all nodes.

Active - passive means only one controller at a time has control, and therefore ALL traffic goes through one node, and only when that node dies do the other contollers take over.

Active - active therefore has a much higher response and better throughput (typically) but they are usually more expensive.

3PAR is Active - Active

Netapp is Active - Passive

Usually....

Expert
Expert

in my experience NetApp is "usually" Active-Active - and NetApp also supports ALUA

It is "possible" to setup 2 netapp heads NOT using a full HA configuration, but anything short of specialized deployments is most likely going to be Active-Active ...

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Immortal
Immortal

Its a bit more indepth than Parker suggests, but not too far.

Here's an article I wrote that goes a bit further on the difference between Active/Active arrays and ALUA array.

http://vmsarefreeright.wordpress.com/2011/07/03/alua-active-arrays/

MANY arrays on the market that call themselves Active/Active are, in fact, ALUA (NetApp, VNX, etc).

There are very few truly active/active arrays - they tend to be, as parker suggests, the more expensive lines (Symmetrix, HDS VSP, 3PAR, etc).

--Matt VCDX #52 blog.cowger.us
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http://vmsarefreeright.wordpress.com/2011/07/03/alua-active-arrays/

thats the article Mcowger is reffering to iirc

--------------------- Sparrowangelstechnology : Vmware lover http://sparrowangelstechnology.blogspot.com
Immortal
Immortal

Indeed.  Thanks!

--Matt VCDX #52 blog.cowger.us
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Enthusiast
Enthusiast

Active-Active  :-  The storage system have two controllers and LUN(Virtual disk or storage device) can be accessed or host can perform I/O via both the controllers.

Active-Passive :- Host can have I/O  to and from one LUN via one controller only (via the active controller- owner - of the LUN and not via the other )

ALUA             :- Asymmetric Logic Unit Access is where the storage system simulates the active-active feature (LUN can be accessed via both controllers but only one will be the owner of it)

  Vipin V.K

Virtuoso
Virtuoso

So in this case, the Active/Active LUN path is the best choice for performance ? or the same as in ALUA pathing ?

/* Any kind of comment or input would be greatly appreciated */
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Virtuoso
Virtuoso

Thanks for the explanation mate,

How about EMC Clariion and VNX series are they Active/Passive or depends on the licensing purchased 🙂

By using the term "node", do you mean the Storage Processor in the Storage Array ?

/* Any kind of comment or input would be greatly appreciated */
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Contributor
Contributor

As some have indicated both the Active/Passive or Active/Active AND the Symmetric or Asymmetric architecture of a system are important considerations. The following is from this HDS publication:  http://www.hds.com/assets/pdf/hitachi-white-paper-dynamic-virtual-controller-technology.pdf

Most midrange storage systems today are dual controllers with an asymmetric active-active architecture, in which both controller nodes are available to process I/Os for their assigned set of LUNs and provide standby capability for the other, non-assigned LUNs. This arrangement requires the administrator to make manual LUN-to-controller assignments based on forecasted workloads. Rebalancing of performance across the controllers as workloads change is also a manual task. Since the performance to a particular LUN is not equal through both controllers, the system is vulnerable to major I/O bottlenecks without an automated means of balancing the load.

Asymmetric active-active architecture can also significantly decrease productivity and increase setup times when matched to VMware environments. For example, the time to configure path failover can take up to 1 hour per physical server. If an organization supports 20 servers, each running 25 VMs, the configuration process can take 2-1/2 days. In a symmetric active-active environment, where the controller removes the need for LUN ownership, the configuration takes less than 5 minutes per server.

Anyone who has to do failover and failback for maintenance and upgrades on kit like NetApp can tell you what a joy that is. 3PAR and HDS both provide the highly desirable symmetric active-active architecture as does the new VNX2 though for now it only does it on basic and not the usually preferable pool LUNs. I do not know about EMC pricing, but 3PAR and HUS systems start at very reasonable price points. I have been on NetApp for the past 8+ years for production and HDS for backup and cannot wait to get onto either 3PAR or an HUS-VM for production. YMMV of course.

Virtuoso
Virtuoso

Wow, so in this case I assume the current EMC VNX is just mid-range Assymmetric Active-Active architecture (because I need to configure or select SPA or SPB manually).

and that does make sense KLStay, the highest range of Storage Array of EMC VMAX should be Symmetric Active/Active, it comes with a price. Smiley Wink

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