Dell Unity: Data Reduction Considerations and Best Practices

In Dell UnityOS 4.3.x and later, the Data Reduction algorithm replaces the traditional Compression algorithm. The Data Reduction algorithm includes deduplication, compression, and zero-block detection.

Keep the following in mind before enabling Data Reduction, enabling Advanced Deduplication, or creating Data Reduction-enabled resources:

• Monitor the system, take note of where the performance metrics stand before enabling Data Reduction or Advanced Deduplication. These increase CPU load on the processors and may lead to data access latency.
• Do not enable Data Reduction on any additional resources if CPU utilization is around 70% or higher.
• Do not enable Data Reduction on any resource when the Write I/O Size is less than 8 KB.

Supported Configurations

"In Dell Unity OE version 4.3 and later, data reduction is supported on Thin LUNs, Thin LUNs within a Consistency Group, Thin File Systems, and Thin VMware VMFS and NFS Datastores. To support data reduction, Thin File storage resources must be created on Dell Unity OE version 4.2 or later and be created within an All Flash Pool. File storage resources created on Dell Unity OE versions prior to version 4.2 do not support data reduction. Within a Consistency Group, data reduction enabled LUNs can be mixed with LUNs which have data reduction disabled. In Dell Unity OE 4.5 and later, Advanced Deduplication is included as an optional feature to the Data Reduction algorithm for configurations that support it."

"In Dell Unity OE 5.2 and later, hybrid (mixed drive type) pools created on Unity XT model systems also support Data Reduction with and without Advanced Deduplication enabled. The pool type can either be Traditional or Dynamic. To support Data Reduction, the pool must contain a flash tier and the total usable capacity of the flash tier must meet or exceed 10% of the total pool capacity. Once a system is upgraded to OE version 5.2 or later, Data Reduction can be enabled on an existing resource if the flash capacity requirement is met."

"Dell Unity Data Reduction and the Advanced Deduplication option, for configurations supporting the Advanced Deduplication feature, can be enabled on supported storage resources at the time of the resource’s creation, or enabled or disabled at a later time. Advanced Deduplication requires Data Reduction to be enabled on the resource but can be enabled or disabled independently to the Data Reduction setting."

Enabling Data Reduction on an Existing Storage Resource

"Dell Unity Data Reduction and/or Advanced Deduplication can be enabled on a supported storage resource at any point in time. This can be completed in Unisphere from the properties window of the storage resource, or by utilizing Unisphere CLI or REST API. Enabling data reduction on File storage resources created prior to OE 4.2 is not supported. When data reduction and/or Advanced Deduplication is enabled on an existing resource, no data on the storage resource is passed through the data reduction algorithm at that time. All previously written data is left in its original state, and only new writes or overwrites are subject to the data reduction algorithm. To achieve savings on existing data within a Block storage resource, the user can utilize the Local LUN Move option, which is outlined below. For File resources, the methods to move File data include host-based migration to a Dell Unity OE 4.2 or later Thin File System, VMware vMotion for VMs created on NFS Datastores, or Dell Unity Asynchronous Replication."

• • All existing data is left unmodified.
  • New data written to the resource is run through the algorithm.
  • Existing data is reduced or compressed when overwritten.

Disabling Data Reduction on a Resource

"As with enabling data reduction, data reduction can be disabled at any point in time on a supported storage resource. Advanced Deduplication can also be disabled at any time without disabling data reduction if required. These operations can be completed in Unisphere from the properties window of the storage resource, or by utilizing Unisphere CLI or REST API."

"If Advanced Deduplication is disabled, all deduplication savings achieved by Advanced Deduplication are unchanged and the data is left in its current state. As data is overwritten, the data is subject to the data reduction algorithm if still enabled or written in its original form if data reduction is disabled."

"If data reduction is disabled, all data for the storage resource is left in its current state within its Pool, whether it is deduplicated, compressed, or not. Data written after disabling data reduction will be stored in its original form. As data that has been deduplicated or compressed is overwritten, data reduction savings are reduced on the storage resource."

"To fully remove data reduction savings from a Block storage resource, Local LUN Move can be utilized by specifying a non-data reduction enabled destination."

• • All existing data is left as reduced or compressed.
  • New data written to the resource is not reduced or compressed.
  • When existing data is overwritten, it is stored in its original form (no reduction).

How to view Data Reduction Savings

• Unisphere UI Pool Savings: STORAGE > Pools > Pool Properties > Usage > General
• Unisphere UI LUN Savings: STORAGE > Block > LUN Properties > General
• Unisphere UI FS Savings: STORAGE > File> FS Properties > General
• Unisphere UI VMware Datastore Savings: STORAGE > VMware > Datastore Properties > General

• uemcli  /stor/config/pool show -detail
• uemcli /stor/prov/luns/lun show -detail
• uemcli  /stor/prov/fs show -detail
• uemcli  /stor/prov/vmware/vmfs show -detail
• uemcli  /stor/prov/vmware/nfs show -detail
• uemcli  /stor/general/system show

Pool Expansion

"In OE versions prior to the 5.2 release, expanding a Pool residing on a Hybrid Flash System which contains data reduction savings is only supported if it is being expanded by supported Flash Drives. For instance, a Pool containing SAS Flash 2 or SAS Flash 3 drives can be expanded by adding more SAS Flash 2 or SAS Flash 3 drives to the Pool. While storage resources exist within the Pool which have data reduction enabled or have had data reduction enabled in the past, adding SAS or NL-SAS drives to convert the Pool to a Hybrid Pool is not supported in OE versions prior to the 5.2 release."

"To expand and convert an All Flash Pool to a Hybrid Pool in OE versions prior to the 5.2 release, all storage resources which have data reduction enabled or have used data reduction must be removed from the Pool. For Block resources, Local LUN Move can be used to move the resource’s data to another resource on the same Pool with data reduction disabled, or to another Pool. When utilizing Local LUN Move to relocate a Block device within the same Pool, you must ensure data reduction is disabled on the destination device. For File resources, the data must be migrated to a new resource, either by leveraging Dell Unity Asynchronous Replication or a host based migration tool. Once all resources which have utilized data reduction have been removed from the Pool, the expansion will be allowed. More information about migration options can be found in the Dell EMC Unity: Migration Technologies white paper found on Dell Technologies Info Hub."

"In OE version 5.2 and later, a Pool containing data reduction enabled resources can be expanded as along as the total capacity of the flash tier is at least 10% of the resulting pool capacity. This means adding SAS or NLSAS drives to convert an All Flash Pool to a Hybrid Pool is supported in OE version 5.2 and later, along with expanding an existing drive tier within the Pool. The pool expansion process is not allowed if the minimum percentage of flash capacity is not met. The minimum Flash requirement is to ensure that Flash capacity is available to store each storage resource’s private space, allowing fast access times during data reduction related updates."

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