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Dell Unity offers an assortment of storage efficiency features that can help you maximize the utilization and performance of your system. The Dell Unity operating environment was built with attention given to the capability of multicore processors and their increasing scale. With the use of Flash media in hybrid system configurations, FAST Cache and FAST VP can ensure that data is readily accessible and is being stored in the right location on the Dell Unity system. Lastly, Host I/O Limits can be implemented to manage host activity and control noisy neighbors.
A set of multicore optimizations is offered on the Dell Unity system:
Multicore optimizations are also found in the implementation of FAST Cache, among other areas within the Dell Unity operating environment.
FAST Cache leverages the performance of Flash media to improve workloads that are interfacing with spinning disk media. FAST Cache is only available for Dell Unity Hybrid systems. FAST Cache is configured on a system-level and can be applied to individual Pools across both block and file resources. Flash drives used by FAST Cache must be of the “SAS Flash 2” type and are configured in mirrored pairs. The maximum capacity of FAST Cache will depend on the system model. For the Pools using FAST Cache, frequently read data from spinning drives (SAS and NL-SAS media) will be copied to FAST Cache so that subsequent access will be sourced from the faster Flash drives. Similarly, frequently rewritten data can be sent from Multicore Cache to FAST Cache, where FAST Cache serves as a secondary, high-capacity cache for the system. FAST Cache is available on purpose-built hybrid Dell Unity systems.
For more information about FAST Cache, see the Dell Unity: FAST Technology Overview white paper.
Fully Automated Storage Tiering for Virtual Pools (FAST VP) ensures your data is distributed effectively across the various media types in a multi-tier pool. FAST VP defines three tiers of drive types:
On a purpose-built Hybrid Dell Unity system, for a Pool with multiple tiers, block and file resources created on that Pool are subject to FAST VP policies. FAST VP policies can specify where the initial data populated to a storage resource should be placed (ex. Highest tier, lowest tier). As the data is manipulated, FAST VP will relocate data across the tiers based on usage (Figure 4).
Data that is being accessed frequently is placed on the best performing tier, while data that has gone “cold” is moved to the high-capacity tiers. Data is relocated at a 256 MB granularity and can be a scheduled recurring event. Combined with FAST Cache and the other multicore optimizations, FAST VP ensures that your drives are being used efficiently.
The ability to limit the amount of I/O activity that is serviced by the Dell Unity system is known as Host I/O Limits. Host I/O Limits can be applied on LUNs, VMware VMFS Datastores, Thin Clones, and their associated attached snapshots. Use Host I/O Limits to limit incoming host activity based on IOPS, Bandwidth, or both. Limits can be enforced on individual resources, or a limit can be shared among a set of resources.
There are several use cases where Host I/O Limits can be effective. Configure Host I/O Limits on LUNs or datastores that are consuming a large portion of the system’s resources and reducing the performance of other resources on the system. This could be the result of a “noisy neighbor” who overruns the provisions set for the multiple tenants accessing data on a system. Another use case for Host I/O Limits is placing limits on attached snapshots. If attached snapshots are being used for backup and testing purposes, Host I/O Limits can be applied to the snapshots to effectively prioritize host activity towards the parent LUNs and datastores.
In Dell Unity OE version 4.1, density-based Host I/O Limits can be created which limits host activity based on the size of the block resource. For example, a density-based I/O limit of 100 IOPS/GB for a 200 GB LUN would result in an overall limit of 20,000 IOPS for the entire LUN. If sometime later the 200 GB LUN was expanded to be a 250GB LUN, the I/O limit would automatically update to 25,000 IOPS for the LUN, saving the administrator managerial tasks and time. Like absolute I/O limits, density based I/O limits can also be shared among multiple resources. Another feature in Dell Unity is burst policies for Host I/O Limits. This option is available for any Host I/O Limit policy and allows host activity/traffic to exceed the base policy limit by a user-specified percentage. The user specifies parameters of amount (percentage), duration, and frequency of the I/O limit burst allowance.
In Dell Unity OE version 4.2, Host I/O Limits were expanded to support Virtual Volumes (vVols). vVols support either an absolute based limit or a density-based Host I/O limit, defined by IOPS or IOPS per GB respectively. Host I/O Limits are supported on data vVols specifically. Host I/O Limits cannot be applied to config, swap, or memory vVols. While the implementation of Host I/O Limits is the same for vVols and Block resources, the management of vVol Host I/O Limits is done entirely through vSphere. Host I/O Limits can be created in vSphere as a rule for a Storage Policy and then assigned at either the VM or vVol level. Unisphere can be used to monitor the vVol, with the capability to display any I/O Limits associated with the vVol as well as real-time performance metrics.
To help reduce the total cost of ownership and increase the efficiency of a Dell Unity storage system, Dell Unity OE version 4.1 introduced Dell Unity Compression for Block resources. Dell Unity OE version 4.2 expanded compression to File resources. With Dell Unity Compression, the amount of space required to store a dataset for compression-enabled storage resources is reduced when savings are achieved. This space savings reduces the amount of physical storage required to store a given dataset, which can lead to cost savings. Dell Unity Compression is available for All Flash pools on either All-Flash or Hybrid Dell Unity systems.
In Dell Unity OE version 4.3, Dell Data Reduction was introduced which replaces Dell Compression. Dell Data Reduction includes deduplication and compression logic within the space savings algorithm. Dell Data Reduction is supported on all resources which support Dell Compression.
In Dell Unity OE version 4.5 and later, Advanced Deduplication is included as an optional feature to the Data Reduction algorithm for the Dell Unity 450F, 550F, 650F, and Dell Unity XT systems. Advanced Deduplication is supported on all resources in a Dynamic Pool that supports Data Reduction and requires Data Reduction to be enabled on the resource. It can be enabled or disabled independently from the Data Reduction setting. Local LUN Move can be leveraged to move a resource’s data into an Advanced Deduplication-enabled resource within an All Flash Pool.
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. 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 percent of the total pool capacity.
Dell Unity Data Reduction is enabled at the resource level, so storage resources with and without data reduction enabled can exist in the same pool on a system. Also, data reduction savings can be seen at multiple levels, including system level, pool level, and resource-level, providing varying levels of granularity in reporting for management purposes.
For more information about Dell Unity Data Reduction or Dell Unity Compression, see the Dell Unity: Data Reduction white paper.