• Introduction to Data Efficiency


    Introduction to Data Efficiency

    Optimizing drive performance using the FAST Cache and FAST VP (supported physical deployments only)

    The FAST (Fully Automated Storage Tiering) Suite includes features that enable you to:

    • Leverage SAS Flash 2 drives as additional read/write cache for improved performance (FAST Cache).
    • Dynamically tier data across different types of drives (FAST VP). FAST VP can use all supported drive types except SAS Flash 4.
    Comparison of FAST Cache and FAST VP

    The following table describes the differences between the FAST Cache and FAST VP features:

    Table 1. Differences between the FAST Cache and FAST VP features
    FAST Cache
    Enables SAS Flash 2 drives to be used as an additional read/write cache for the storage system.
    Leverages pools to provide sub-LUN and file system tiering, which moves data to the appropriate tier based on the FAST VP tiering policy.
    Caches 64-KB data chunks for higher performance.
    Relocates 256-MB data chunks based on the FAST VP tiering policy and I/O activity.
    Copies data from Hard Disk Drives (HDDs) to Flash drives when the data is accessed frequently.
    Moves data between different storage tiers based on the FAST VP tiering policy.
    Adapts continuously to changes in workload.
    Uses a data relocation process to periodically make storage tiering adjustments. The data relocation schedule is configurable, and the data relocation can take place once a day or on an ongoing basis throughout the day.
    Interoperability considerations

    You can use FAST Cache and FAST VP functionality together to yield high performance and improve Total Cost of Ownership (TCO) for the storage system. It is recommended that you:

    1. Use available SAS Flash 2 drives for the FAST Cache first, because this can benefit all storage resources in the storage system.
    2. Supplement performance as needed by adding additional SAS Flash 2 drives to pool tiers for use by FAST VP.

    For example, in scenarios where limited SAS Flash 2 drives are available, you can use SAS Flash 2 drives to create the FAST Cache, and you can apply FAST VP on a one- or two-tier pool (SAS and NL-SAS). From a performance point of view, FAST Cache dynamically provides performance benefits to bursts of data, while FAST VP moves "hotter" data to performance drives and "colder" data to capacity drives. From a TCO perspective, FAST Cache, with a small number of Flash drives, serves the data that is accessed most frequently, while FAST VP optimizes drive utilization and efficiency.

    The FAST Cache feature is storage-tier-aware and works with FAST VP to make sure that the storage system resources are not wasted by unnecessarily copying data to FAST Cache, if it is already on a Flash drive. If FAST VP moves a chunk of data to the Extreme Performance Tier on a pool, the system will not copy that chunk of data into FAST Cache, even if FAST Cache criteria is met for promotion. This ensures that the storage system resources are not wasted in copying data from one Flash drive to another.

    Automatic snapshot deletion

    Automatic snapshot deletion is a space management feature used to automatically manage the number of snapshots in a pool. This feature is triggered when the total pool consumption or pool consumption by the snapshots reach a high threshold you define. The system automatically starts deleting old and expired snapshots until the pool space reaches a set threshold.

    Expired snapshots are deleted first. If deleting the expired snapshots does not still result in reaching the thresholds, the system starts deleting the detached oldest snapshots with the automatic deletion option enabled. Automatic deletion does not apply to snapshots attached to hosts, including attached groups of snapshots on a consistency group. It also does not apply to system snapshots used for replication.

    You can set a snapshot of a storage resource for automatic deletion when the snapshot expires (by setting a snapshot expiration date) or the associated pool reaches the auto delete threshold settings. The following table explains the automatic snapshot deletion options:

    Note:  If a snapshot has automatic snapshot deletion enabled, it cannot be used as a source snapshot for creating or refreshing a thin clone.
    Table 2. Automatic snapshot deletion options
    Applies to snapshots of storage resources and pools. When the pool reaches a certain threshold, the system automatically deletes the snapshot.
    Expiration time
    Applies to snapshots of storage resources. This is the time when the snapshot expires.

    About data reduction

    Applying data reduction saves space on the system. Data reduction includes savings from deduplicating blocks which contain internally-defined data patterns, including zero detection and compression. Data reduction is available for thin LUNs, thin file systems, and thin NFS and VMFS datastores created in All-Flash pools. The thin file system must be created on a Unity system that is running OE version 4.2.x or later.

    A single switch called Data Reduction controls deduplication of the blocks at an individual LUN and file system level. Adding a subsequent switch called Advanced Deduplication controls a deeper, dynamic ability for deduplicating data blocks within a given storage resource that do not contain internally-defined data patterns.

    Data reduction is applied on all new incoming writes. Data that cannot be deduplicated or compressed is detected, and is written uncompressed.

    Data that already exists on a LUN will not have data reduction applied after data reduction is enabled. In order to apply data reduction to existing LUN data, you must use the LUN Move feature to move the LUN's data to a destination LUN that has data reduction enabled.

    The Advanced Deduplication option helps increase the storage efficiency of systems above what is achieved with data reduction on a LUN, file system, or datastore. It provides the ability to reduce the amount of storage needed for user data by keeping only a small number of copies (often just one copy) of a data block with a given content. Advanced deduplication can be enabled only if data reduction is enabled first.

    The Advanced Deduplication switch is available only on:

    • Dynamic or Traditional pools in Unity 380F, 480F, 680F, and 880F systems
    • Dynamic pools in Unity All-Flash 450F, 550F, and 650F systems
    • All-Flash pools in Unity Hybrid 380, 480, 680, and 880 systems

    If you need to convert an All-Flash pool to a hybrid pool (adding non-Flash drives to an All-Flash pool), any LUNs, file systems, or datastores that use data reduction must be deleted or moved. Hybrid pools cannot have data reduction enabled, and you cannot create a data reduction-enabled LUN, file system, or datastore in a hybrid pool. An All-Flash pool can contain both data reduction-enabled and non-data reduction enabled LUNs, file systems, or datastores.

    For additional information, refer to the Dell EMC Unity: Data Reduction white paper.