D-PWF-DS-23 Questions and Answers

By changing the granularity of the PowerFlex storage pool from fine to medium, the architect improved the performance of the system. Medium Granularity (MG) storage pools are recommended for environments where I/O performance and low latency are critical, such as Virtual Desktop Infrastructure (VDI) deployments1.

Here’s a detailed explanation of the change:

• Fine Granularity (FG): FG storage pools are designed for space efficiency and enable features like inline compression, which can reduce the size of volume data depending on its compressibility.However, this can come at the cost of performance due to the overhead of compression and the smaller space allocation block size2.
• Medium Granularity (MG): MG storage pools, on the other hand, provide supreme I/O performance with the least latency to virtual machines and applications. They use a larger space allocation block size of 1 MB, which is more efficient for I/O operations compared to the 4 KB block size used in FG storage pools1.
• Performance Improvement: By switching to an MG storage pool, the architect ensured that the storage volumes provide better I/O performance and lower latency, which is essential for applications that require fast and responsive storage access1.

This change aligns with the best practices for PowerFlex storage provisioning, where the selection of granularity is based on the specific performance and space efficiency needs of the customer’s workload1.

To calculate the required journal capacity, we need to consider the maximum cumulative writes that might occur during an outage. The calculation is based on the application’s write bandwidth and the duration of the supported outage. For an application generating 2 GB/s of writes, using a 2-hour outage (which is 7200 seconds), the journal capacity reservation needed is:

Journal Capacity=Write Bandwidth×Outage Duration

Journal Capacity=2 GB/s×7200 s=14400 GB

However, since the question specifies that the outage is under two hours, we use the minimum outage allowance of 1 hour for the calculation, which is 3600 seconds. Therefore, the correct calculation is:

Journal Capacity=2 GB/s×3600 s=7200 GB

But considering the recommendation to use three hours in the calculations for safety, the needed capacity would be approximately 10.547 TB, which is roughly 10.800 GB12. Hence, the verified answer is 10.800 GB.

The maximum number of Storage Data Servers (SDSs) per protection domain in a PowerFlex rack is 1283. This is specified in the PowerFlex specification sheet and ensures that each protection domain can provide data protection for a significant number of SDSs, allowing for scalability and resilience within the PowerFlex infrastructure.

Secure snapshots in PowerFlex are controlled by policies that define their retention and expiration periods. If a snapshot has a lock enabled, it cannot be deleted until the lock is disabled. The lock is a security feature that prevents accidental or unauthorized deletion of the snapshot before its intended retention period1.

To delete a secure snapshot that is still within its expiration period but needs to be removed, the administrator must first disable the snapshot policy lock. Here are the general steps to do so:

• Access PowerFlex Manager.
• Navigate to the Snapshots section.
• Locate the specific snapshot that needs to be deleted.
• Disable the lock on the snapshot policy associated with the snapshot.
• Once the lock is disabled, the snapshot can be deleted manually.

Changing the snapshot expiration period to 30 days (Option C) would not affect the ability to delete the snapshot if the lock is still enabled. The Dual Signature Policy agreement with Dell (Option A) is not a standard procedure for deleting snapshots within PowerFlex and is not related to the administrative controls of snapshot policies.

Therefore, the correct answer is B. Disable the snapshot policy lock on the snapshot, as this action will allow the administrator to delete the snapshot before the expiration period, provided that the snapshot is no longer needed and can be safely removed from the system1.

Volume migration in PowerFlex allows for the movement of volumes between storage pools, which can be necessary for various operational reasons such as performance tuning, capacity expansion, or infrastructure upgrades. The possible migrations are:

• Option B: Migrating from an MG (Medium Granularity) storage pool volume that is zero padded and thick provisioned to an FG (Fine Granularity) storage pool volume that is also zero padded and thin provisioned. This migration is possible and allows for a change in the provisioning and granularity of the volume, which can be beneficial for optimizing storage efficiency and performance1.
• Option D: Migrating from an MG storage pool volume that is non-zero padded and thin provisioned to another MG storage pool volume that is zero padded and thin provisioned. This migration is within the same granularity type (MG) and involves changing the padding of the volume. It is a viable option when adjusting the volume configuration for specific storage optimization needs1.

These migrations are supported by PowerFlex’s flexible architecture, which allows for non-disruptive volume movements between storage pools. The process involves using PowerFlex’s management tools to initiate and monitor the migration, ensuring data integrity and system stability throughout the operation1.

The references for these migrations come from PowerFlex documentation and best practices, which detail the procedures and capabilities of the system regarding volume management and migration1. It isimportant to follow the recommended guidelines to ensure successful migrations that align with the system’s design and operational principles.

When expanding a PowerFlex rack solution, optimizing the redundancy of the MDM roles is crucial to maintain system resilience and availability. The best practice in such a scenario is to distribute the MDM roles across the available cabinets to prevent a single point of failure. This can be achieved by adding Standby MDMs to the newly added cabinets1.

Here’s a step-by-step explanation:

• Assess the current MDM configuration: Understand the current setup of MDMs and Tie-breakers in the existing cabinets.
• Plan for distribution: Decide on how to distribute the MDM roles across the expanded infrastructure to enhance redundancy.
• Add Standby MDMs: Introduce Standby MDMs in the new cabinets (Cabinet 3, Cabinet 4, and Cabinet 5) to ensure that each cabinet has an MDM role, enhancing the fault tolerance of the system.
• Configure Standby MDMs: Properly configure the Standby MDMs to take over in case the Primary or Secondary MDMs fail.
• Test the configuration: After adding the Standby MDMs, test the system to ensure that the MDM roles can failover smoothly without impacting the system’s performance or availability.

By adding Standby MDMs to the new cabinets, you ensure that the MDM roles are not concentrated in a single cabinet, which could lead to a higher risk of system downtime if that particular cabinet encounters issues. This approach aligns with the best practices for designing resilient and high-availability systems1.

The other options do not provide the same level of redundancy optimization. For instance, moving MDM 3, Tie-breaker 1, and Tie-breaker 2 to separate cabinets (Option A) does not address the need for additional Standby MDMs in the new cabinets. Changing the MDM Cluster Mode from three-node to five-node (Option C) is not necessary for redundancy and may introduce unnecessary complexity. Consolidating MDM 2 and Tie-breaker 1 into Cabinet 1 (Option D) would reduce redundancy rather than optimize it.

Therefore, the correct answer is B. Add Standby MDMs to Cabinet 3, Cabinet 4, and Cabinet 5, as it provides a distributed and resilient MDM configuration suitable for an expanded PowerFlex rack solution.

To track total usage on a PowerFlex File system without imposing any restrictions on users, an administrator can create a tree quota and set both the soft and hard limits to zero. This method allows the administrator to monitor usage without enforcing any quota limits, thus not restricting user behavior.

Here’s how it can be accomplished:

• Access the PowerFlex Management Console: Log in to the PowerFlex Management Console where you can manage quotas.
• Navigate to the File System: Locate the file system for which you want to track usage.
• Create a Tree Quota: Choose to create a new tree quota for the file system.
• Set Limits to Zero: When setting up the quota, input zero for both the soft and hard limits. This effectively means there are no limits enforced on the users.
• Apply the Quota: Save and apply the quota settings to the file system.

By setting both limits to zero, the administrator can use the quota system purely for monitoring purposes, without affecting user operations. The users will not encounter any quota warnings or limits, but the system will still track and report on the total usage, which the administrator can review.

The rationale behind using a tree quota rather than a user quota is that tree quotas are associated with a directory tree, allowing the tracking of usage across a broader scope, which is more suitable for monitoring overall file system usage.

This approach is consistent with best practices for administering PowerFlex systems as described in the Dell PowerFlex Administration Guide1, which provides detailed procedures for managing storage, including the configuration of quotas for monitoring purposes.