We have storage array product from different vendor. Everyone talkes about active-active and active-passive device technology. With different types of storage arrays and host connection types, it is important to understand the difference between active-active and active-passive devices. Here is short explanation of the differences:
Active-active (for example, Symmetrix arrays)
In an active-active storage system, if there are multiple interfaces to a logical device, they all provide equal access to the logical device. Active-active means that all interfaces to a device are active simultaneously.
Active-passive (for example, CLARiiON arrays)
Active-passive means that only one interface to a device is active at a time, and any others are passive with respect to that device and waiting to take over if needed.
In an active-passive storage system, if there are multiple interfaces to a logical device, one of them is designated as the primary route to the device (that is, the device is assigned to that interface card). Typically, assigned devices are distributed equally among interface cards. I/O is not directed to paths connected to a non-assigned interface. Normal access to a device through any interface card other than its assigned one is either impossible (for example, on CLARiiON arrays) or possible, but much slower than access through the assigned interface card.
In the event of a failure, logical devices must be moved to another interface. If an interface card fails, logical devices are reassigned from the broken interface to another interface. This reassignment is initiated by the other, functioning interface. If all paths from a host to an interface fail, logical devices accessed on those paths are reassigned to another interface with which the host can still communicate. EitherApplication-Transparent Failover (ATF) or PowerPath, which instructs the storage system to make the reassignment, initiates this reassignment. These reassignments are known as trespassing. Trespassing can take several seconds to complete. However, I/Os do not fail during it. After devices are trespassed, ATF or PowerPath detects the changes and seamlessly routes data via the new route. After a trespass, logical devices can be trespassed back to their assigned interface. This occurs automatically if PowerPath's periodic autorestore feature is enabled. It occurs manually if powermt restore is run, which is the faster approach. Or if ATF is in use, a manual restore of the path can be executed to restore the original path.

2 Comments:

  1. Storage Machine Says:
  2. Is CX4 also active-passive storage system?

  3. Anonymous Says:
  4. Yes, CX4 is also an Active-Passive array.

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