DEE-1111 Expert - PowerMax and VMAX All Flash Solutions Questions and Answers

In an SRDF/Star configuration, all SRDF/Star device pairs must be of the same geometry and size. This is because SRDF/Star uses concurrent SRDF to maintain synchronous and asynchronous SRDF sessions between three arrays. The devices in these sessions must have identical geometry to ensure data consistency56. References: Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide, SRDF/Metro overview | Dell EMC PowerMax and VMAX All Flash: SRDF/Metro Overview and Best Practices

Data Domain is the only external storage that can be connected to PowerMax using DX emulation. DX emulation is a specialized back-end DA emulation that handles SAN attached disks. DX directors are configured on existing PowerMax front-end Fibre Channel ports and are required to be implemented in pairs for high availability. DX emulation is used to support ProtectPoint technology, which integrates primary storage with Data Domain protection storage to accelerate backup and recovery. Therefore, answer A is correct1.

B, C, and D are incorrect because they are not external storage that can be connected to PowerMax using DX emulation. Unity (B), PowerStore ©, and Compellent (D) are primary storage arrays that do not support ProtectPoint technology or DX emulation.

In a Concurrent SRDF/Star environment where the production data on R11 devices are replicated to two R2 devices in two remote arrays, SRDF/S links must be configured between Site 3 and Site 2. This is because in a Concurrent SRDF/Star configuration, there are two target sites and one source site. If there’s a failure, the source site can switch to either of the target sites based on the business continuity plan1. References: Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide, SRDF Star software uses and best practices - Dell

he %Busy and Balance KPIs are the most important indicators of the BE performance on a PowerMax array. The %Busy metric shows the percentage of time that a BE director is busy processing I/O requests. A high %Busy value may indicate that the BE director is overloaded and cannot keep up with the demand. The Balance metric shows the difference in %Busy between the two BE directors in a pair. A high Balance value may indicate that the workload is not evenly distributed across the pair, which can lead to performance degradation. By monitoring these two KPIs, a storage administrator can identify and troubleshoot any potential issues with the BE performance.

References:

• PowerMax Performance Troubleshooting with Unisphere - Run a real time trace at the system level

A noisy neighbor issue occurs when one or more applications consume more resources than expected, causing performance degradation for other applications. This can affect the SL compliance of a storage group, as the service level defines the expected response time and performance for the applications in that group. If a noisy neighbor consumes too much cache, bandwidth, or CPU cycles, it can cause the SL compliance to drop below the target level. Therefore, answer A is correct.

B, C, and D are incorrect because they are not likely to cause SL compliance impact for a storage group. Queue depth full event (B) is a host-side issue that occurs when the host queue depth is too low or the host I/O rate is too high, causing the host to stop sending I/O requests to the array. Host queue depth setting © is also a host-side parameter that determines how many I/O requests can be queued by the host. Performance thresholds (D) are user-defined values that trigger alerts when certain metrics exceed or fall below the specified levels. None of these factors affect the SL compliance of a storage group on the array.

When the RDF-ECA timer expires, all RDF links will be in a ‘Suspend’ state. This is because the RDF-ECA timer is used to control how long SRDF waits for an acknowledgement from the remote array before it suspends the link. If an acknowledgement is not received within this time, SRDF assumes that there is a problem with the link or remote array and suspends the link to prevent data loss or corruption.

The correct sequence of actions that take place on a Write Miss is as follows:

• Host sends requests to FE director and no cache slots are found.This happens when the cache is full or the desired cache slot is locked by another request1.
• FE finds available slot by polling.This involves the FE director scanning the cache for an available slot or waiting for a slot to be freed by the BE director2.
• FE sends data from host to mirrored cache locations.This involves the FE director writing the data from the host to two mirrored locations in the cache, one on each engine2.
• FE responds to host to acknowledge successful write.This involves the FE director sending a signal to the host that the write operation is completed, even though the data is not yet written to disk2.
• BE destages data as a high-priority task to make slots available.This involves the BE director flushing some of the existing write pending data from the cache to the disk, in order to free up some cache slots for new write requests2.
• BE destages new data to disk at a later time.This involves the BE director writing the new data from the cache to the disk, according to the destaging algorithm and priority2.

SRDF device used for Concurrent SRDF environments =R21

SRDF device used for SRDF/Star environments =R11

SRDF device used for Cascaded SRDF environments =R22

A dual personality SRDF device is a device that can act as both an R1 and an R2 device in different SRDF configurations. There are three types of dual personality SRDF devices: R21, R11, and R22.

• An R21 device is an R2 device that is paired with another R1 device in a different SRDF group. This allows the R21 device to receive updates from the primary site and send updates to the secondary site. An R21 device is used for Concurrent SRDF environments, which provide simultaneous disaster recovery and data migration capabilities.For example, an R21 device can be used to migrate data from one array to another while maintaining a synchronous copy of the data on a third array.1
• An R11 device is an R1 device that is paired with another R1 device in a different SRDF group. This allows the R11 device to receive updates from the primary site and send updates to the tertiary site. An R11 device is used for SRDF/Star environments, which provide three-site disaster recovery capabilities with a single hop between any two sites.For example, an R11 device can be used to create a synchronous copy of the data on a secondary site and an asynchronous copy of the data on a tertiary site.2
• An R22 device is an R2 device that is paired with another R2 device in a different SRDF group. This allows the R22 device to receive updates from the secondary site and send updates to the tertiary site. An R22 device is used for Cascaded SRDF environments, which provide three-site disaster recovery capabilities with two hops between the primary and tertiary sites.For example, an R22 device can be used to create an asynchronous copy of the data on a secondary site and another asynchronous copy of the data on a tertiary site.3

References:

• Dell EMC SRDF Introduction - Dell Technologies Partner Portal
• Dell EMC PowerMax and VMAX All Flash: SRDF Product Guide
• Dell EMC PowerMaxOS Performance Guide

During a Non-Disruptive Migration (NDM), issuing the ReadyTgt SYMCLI command to the migrating Storage Group completes the migration by removing the migrated application resources from the source array2. This command is typically issued after all data has been synchronized from the source to the target array and application I/O has been switched to thetarget array2. References: NDM overview | Dell EMC PowerMax and VMAX: Non-Disruptive Migration Best Practices and Operational Guide | Dell Technologies Info Hub

 In an SRDF/Metro configuration with bias setting, if there is a failure at the R1 array (which is configured as the bias side), the R2 device automatically becomes the active device. This means that even if there’s a failure on the R1 side, operations can continue on the R2 side without interruption, ensuring high availability.

https://infohub.delltechnologies.com/l/dell-emc-powermax-and-vmax-all-flash-srdf-metro-overview-and-best-practices-1/understanding-bias

When expanding the capacity of a three-brick PowerMax 8000 running PowerMaxOS 5978.444.444 configured with Flash Drives RAID 5 (7+1) with SCM drives, the minimum supported configuration is 1x RAID 5 (7+1) added to each brick. This ensures that each brick has additional capacity and maintains the balance of storage across all bricks2. References: Dell EMC PowerMax Family Product Guide PowerMaxOS, Dell PowerMax Family Site Planning Guide PowerMax 2000 and PowerMax 8000, POWERMAX FAMILY PowerMax 2000 and 8000 - Dell Technologies Partner Portal

The minimum number of samples that must be collected via a single Real Time Trace collection process in Unisphere for PowerMax is 1040. This is because the Real Time Trace feature allows the user to collect performance data at 30-second intervals for up to 8 hours, which results in 1040 samples (8 x 60 x 60 / 30 = 1040). The Real Time Trace feature can be used to monitor the performance of storage groups, directors, ports, or devices at a granular level and identify any potential issues or bottlenecks.

References:

• PowerMax Real Time SG Monitoring in Unisphere 9 0
• VMAX Performance Troubleshooting with Unisphere - Run a real time trace at the system level

 In PowerMax, each RAID group is divided into 64 logical blocks known as TDATs (Thin Device Addressable Tracks). Each TDAT is configured to hold data at a given data reduction level, from 1:1 uncompressed data all the way to 16:11. References: Data Protection Schemes | Dell PowerMax: Reliability, Availability, and Serviceability | Dell Technologies Info Hub