Ask the Expert

Active/active vs. active/passive arrays

What are the differences between active/active and active/passive arrays? Which technology is better?

Requires Free Membership to View

Storage arrays (SCSI, Fibre Channel, iSCSI and NAS) with two or dual controllers (or more) can be configured in either an active/active mode or active/passive mode.

Active/passive means that one controller is active to process I/O requests, while the other is idle in standby mode ready to take over I/O activity should the active primary controller fail or be taken offline. An active/active configuration enables both controller nodes to process I/Os, and provide a standby capability for the other.

Generally, an active/active storage system involves a battery backed mirrored cache, in which the contents of a controller's cache is mirrored to another for data integrity and availability. For example, if an active/active controller has a total of 4 gigabytes (GB) of cache (e.g., 2 GB per controller), the usable amount of cache would be 50% or 2 GB due to mirroring.

Typically, a LUN will be accessed primarily via a specific controller to maintain cache coherency in what is known as LUN or cache affinity. Some controllers enable either controller to respond to a server's request for an I/O for a LUN. However, the actual I/O is resolved by a designated controller in what is known as I/O shipping. As to which approach is better, if you can afford to have one controller idle, an active/passive configuration gives predictable performance during a failover. Many NAS vendors use this model, which is often referred to as a NAS cluster. An active/active configuration enables both controllers to be active to boost performance during normal operation. However, during a failover scenario depending on the combined workload, performance could degrade.

Do you know…

How to decrease I/O latency in RAID array?

This was first published in July 2006

There are Comments. Add yours.

TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to: