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

The feature of PowerMax and VMAX All Flash arrays that provides ORM functionality is write coalescing. ORM stands for Optimized Resource Management, which is a set of technologies that optimize the performance and efficiency of flash storage. Write coalescing is one of the ORM technologies that reduces the write amplification and extends the life of flash drives. Write coalescing combines multiple small writes into larger sequential writes before destaging them to the flash drives. This reduces the number of write operations and the amount of data that needs to be erased and rewritten on the flash drives, which improves the performance and endurance of the flash storage.

References:

• Dell EMC PowerMax: Family Overview
• Dell EMC PowerMax and VMAX All Flash: Data Reduction
• Dell EMC PowerMax and VMAX All Flash: Embedded Management

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

The maximum retention period for the SLO Compliance Report is 6 months. This means that data older than 6 months will not be available in the report

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

An application owner is experiencing performance issues for their application. Unisphere for PowerMax is showing the storage group is compliant with the current Service Level. This means that the performance issue is not caused by the storage system, but by some other factor in the environment, such as network congestion, host configuration, or application workload. One possible way to address the performance issue is to redistribute the application to other front-end host ports on different directors. This can help balance the workload across multiple paths and avoid potential bottlenecks or contention on a single port or director. Unisphere for PowerMax provides a Performance Plan feature that can analyze the current configuration and suggest optimal port allocation for each storage group based on historical data and best practices.

References:

• Understanding Performance Management
• Dell EMC PowerMaxOS Performance Guide

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

 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

A company plans to implement SRDF/Star, which is a three-site replication solution that provides continuous data protection and disaster recovery capabilities. It is currently using SRDF/S between their two data centers, which are located within 200 kilometersand use synchronous replication. It is setting up a third data center and wants to have at least two identical copies of its data in case of a primary site failure. The third site can be located anywhere in the world and use asynchronous replication. The condition that is needed for the connection between the first two sites and the third site is that the link must be able to transport the delta set of the Recovery Point Objective (RPO) within the company’s Recovery Time Objective (RTO). The delta set is the amount of data that has changed since the last successful replication cycle. The RPO is the maximum acceptable amount of data loss measured in time. The RTO is the maximum acceptable amount of time to restore normal operations after a disaster. The link must have enough bandwidth and latency to ensure that the delta set can be transferred within the RTO without exceeding the RPO.

References:

• SRDF Star software uses and best practices
• SRDF/STAR
• Remote replication using SRDF

https://infohub.delltechnologies.com/l/dell-emc-powermax-and-vmax-non-disruptive-migration-best-practices-and-operational-guide-1/ndm-overview

The symaudit -list command is used to display audit records for SYMCLI commands. The exhibit shows the output of the symauth -list command, which displays the user groups and access types defined for SYMCLI commands. The output shows that there are two user groups: AdminGrp and EmcMgmtGrp. The AdminGrp group has ADMINRD access type, which means that users in this group can run any SYMCLI command with read-only access. The EmcMgmtGrp group has BASECONTROL access type, which means that users in this group can run only a subset of SYMCLI commands with read/write access. However, the output also shows that there are two exceptions for specific users: Beth and Frank. Beth has ADMINRD access type for all commands, which overrides her membership in EmcMgmtGrp group. Frank has BASECONTROL access type for all commands, which overrides his membership in AdminGrp group. Therefore, the only user who has access to run the symaudit -list command based on the symauth output shown in the exhibit is Beth, since she has ADMINRD access type for all commands2

 When the cache space fills up, I/O will be queued until an empty cache slot is available. This is because PowerMax operates as a cache-centric architecture, where all data is passed through cache before being stored on disk. Cache is used to buffer incoming and outgoing data, as well as to support various functions such as replication and data reduction. When cache is full, the array cannot accept any more data until some cache slots are freed up by flushing data to disk or invalidating stale data. Therefore, answer B is correct.

A, C, and D are incorrect because they do not describe what happens when cache space fills up. I/O will not be serviced at the speed of the destination device (A), as this would bypass the cache and degrade performance. Cache is not permanently flushed © or temporarily disabled (D), as this would result in data loss or corruption.

The correct sequence of steps to configure and bring up an SRDF/Star environment is as follows:

• Verify SRDF/Star control host connectivity and array settings. This step involves checking the network connectivity between the control host and the three arrays involved in the SRDF/Star configuration, as well as verifying the array settings such as RDF mode, RDF consistency, and RDF emulation. The control host is the host that runs the Solutions Enabler SYMCLI commands to manage the SRDF/Star configuration.The three arrays are the primary array, the secondary array, and the tertiary array.1
• Enable SRDF/Star configuration. This step involves enabling the SRDF/Star feature on the primary array using the symstar enable command. This command also creates a STAR control device group on the primary array, which contains a single device that acts as a control point for the SRDF/Star configuration.The STAR control device group must have a unique name and number across all arrays.1
• Add BCV devices to the SRDF/Star configuration. This step involves adding Business Continuance Volume (BCV) devices to the STAR control device group on the primary array using the symstar add bcv command. BCV devices are local copies of data that can be used for backup, restore, or testing purposes. BCV devices are required for SRDF/Star configurations to enable fast recovery in case of a disaster.The number of BCV devices must match the number of R1 devices in the SRDF/Star configuration.1
• Create an SRDF/Star composite group and options file. This step involves creating an SRDF/Star composite group on the control host using the symstar create command. An SRDF/Star composite group is a logical grouping of devices that span across three arrays and have different SRDF roles: R11, R21, and R22. An R11 device is an R1 device that is paired with another R1 device in a different SRDF group. An R21 device is an R2 device that is paired with another R1 device in a different SRDF group. An R22 device is an R2 device that is paired with another R2 device in a different SRDF group.The symstar create command also creates an options file that contains various parameters for the SRDF/Star configuration, such as RDF mode, RDF consistency, RDF emulation, and bias setting.1
• Perform the symstar setup operation and create composite groups on target sites. This step involves performing the symstar setup operation on the control host using the symstar setup command. This command establishes the SRDF/Star configuration by creating RDF pairs between devices in different arrays, creating RDF groups on each array, creating composite groups on each array, and synchronizing data across all devices.The symstar setup command also creates composite groups on the secondary and tertiary arrays using the same name and number as the composite group on the primary array.1

References:

• Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

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.