To improve system redundancy using the grid architecture of an IBM XIV Storage System, where in the XIV system can a partition be mirrored?

Introduction / Context:
This question highlights redundancy in IBM XIV Storage System grid architecture. XIV spreads data across many modules, each with its own disks and processing resources. Mirroring partitions across modules rather than within a single module is key to surviving individual module or disk failures.

Given Data / Assumptions:

The storage platform is IBM XIV with a grid of identical modules.

Partitions, or logical volumes, can be mirrored for redundancy.

The goal is to improve system redundancy, not just protect against single disk failure within one module.

Mirroring across modules is supported by the XIV design.

Concept / Approach:
In a grid storage system, mirroring across modules ensures that the loss of a module or several disks in that module does not cause data loss. Placing both copies of data on the same disk or even only within one module would leave the system vulnerable to module level failures. Therefore, mirroring partitions on disks in other modules is a core design principle that enhances overall redundancy and availability.

Step-by-Step Solution:
1. Consider the impact of mirroring a partition on the same physical disk, which provides almost no real redundancy. 2. Consider mirroring only within the same module. This may protect against some disk failures but not against a module outage. 3. Recognize that placing mirrored copies on disks in different modules protects against the loss of an entire module. 4. Evaluate the options and identify the one that explicitly mentions mirroring on disks in other modules. 5. Select the option that aligns with the grid architecture philosophy of distributing data across modules for resiliency.

Verification / Alternative check:
Product documentation for XIV explains that data is spread across all modules and that redundancy schemes place copies on different modules to provide tolerance for module and disk failures.

Why Other Options Are Wrong:
Mirroring on the same disk does not protect against disk failure and defeats the purpose of redundancy.
Mirroring only within a single module does not guard against a complete module loss due to hardware issues or maintenance events.
The option that suggests putting copies on the same disk, the same module, and other modules at once is not realistic and would waste capacity without clear benefit.

Common Pitfalls:
A common misunderstanding is equating mirroring with any duplication, without considering failure domains. Effective redundancy must cross failure domains, such as disks and modules, rather than remain inside a single component. Grid architectures are designed to spread risk and workload widely.

Final Answer:
To improve redundancy, a partition is mirrored on disks that reside in other modules within the XIV grid.