Active vs Passive vs ALUA Storage

[robadawb]

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?

[RParker]

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....

[TedH256]

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 ...

[vAdmin]

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 ?

[mcowger]

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).

[sparrowangelste]

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

thats the article Mcowger is reffering to iirc

[mcowger]

Indeed.  Thanks!

[vipinvk]

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

[vAdmin]

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

[klstay]

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.

[vAdmin]

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. :smileywink: