Unity Implementation (BEST PRACTICES) STORAGE CONFIGURATION

DYNAMIC POOLS

Dynamic Storage Pools apply RAID protection to groups of drive extents from drives within the pool, and allow for greater flexibility in managing and expanding the pool. Dynamic pools are only available on Unity all-Flash systems, and therefore must be all-Flash pools; dynamic pools cannot be built with HDDs.

TRADITIONAL POOLS

Traditional Storage Pools apply RAID protection to discreet groups of drives within the storage pool. Traditional pools are the only type of pool available on Unity hybrid systems, and are also available on all-Flash systems.

ALL-FLASH POOL

All-Flash pools provide the highest level of performance in Dell EMC Unity. Use an all-Flash pool when the application requires the highest storage performance at the lowest response time. Snapshots and Replication operate most efficiently in all-Flash pools. Data Reduction is only supported in an all-Flash pool. FAST Cache and FAST VP are not applicable to all-Flash pools. Dell EMC recommends using only a single drive size and a single RAID width within an all-Flash pool. EXAMPLE: For an all-Flash pool, use only 1.6TB SAS Flash 3 drives, and configure them all with RAID-5 8+1.

RAID PROTECTION (dynamic pools)

At the time of creation, dynamic pools will use the largest RAID width possible with the number of drives specified, up to the following maximum widths: • RAID-1/0: 4+4 • RAID-5: 12+1 • RAID-6: 14+2 With dynamic pools, there is no performance or availability advantage to smaller RAID widths. Therefore, to maximize usable capacity with parity RAID, it is recommended to initially create the pool with enough drives to guarantee the largest possible RAID width. • For RAID-5, initially create the pool with at least 14 drives • For RAID-6, initially create the pool with at least 17 drives.

RAID PROTECTION

Dell EMC Unity applies RAID protection to the storage pool in order to protect user data against drive failures. Choose the RAID type that best suits your needs for performance, protection, and cost: • RAID-1/0 provides the highest level of performance from a given set of drive resources, with the lowest CPU requirements; however, only 50% of the total drive capacity is usable • RAID-5 provides the best usable capacity from a set of drive resources, but at lower overall performance and availability than RAID-1/0 • RAID-6 provides better availability than RAID-5 and better usable capacity than RAID-1/0, but has the lowest performance potential of the three RAID types

RAID PROTECTION (traditional pools)

For traditional pools, Dell EMC generally recommends RAID-5 for drives in Extreme Performance and Performance tiers, and RAID-6 for drives in the Capacity tier. Assuming that roughly the same number of drives will be configured in a traditional pool, Dell EMC generally recommends smaller RAID widths as providing the best performance and availability, at the cost of slightly less usable capacity. EXAMPLE: When configuring a traditional pool tier with RAID-6, use 4+2 or 6+2 as opposed to 10+2 or 14+2. When choosing RAID-1/0, 1+1 can provide better performance with the same availability and usable capacity as larger RAID widths (assuming that the same total number of drives are used), and also provides more flexibility.

SPARE CAPACITY

Hot spares are not needed with dynamic pools. A dynamic pool will automatically reserve spare space in the pool at a rate of 1 drive's worth of capacity per every 32 drives. In the event of a drive failure, the data that was on the failed drive is rebuilt into the spare capacity on the other drives in the pool. Additionally, un-bound drives of the appropriate type can be used to replenish a pool's spare capacity, after the pool rebuild has occurred.

HYBRID POOL

Hybrid pools can contain HDDs (SAS and NL-SAS drives) and Flash, and can contain more than one type of drive technology in different tiers. Hybrid pools typically provide greater capacity at a lower cost than all-Flash pools, but also typically have lower overall performance and higher response times. Use hybrid pools for applications that do not require consistently low response times, or that have large amounts of mostly inactive data. Dell EMC recommends provisioning a Flash tier in hybrid pools. The Flash tier helps enable pool performance efficiencies, and improves response times when using Snapshots and/or Replication. The minimum recommended Flash capacity is at least 5% of the pool capacity. Performance of a hybrid pool can be improved by increasing the amount of capacity in the Flash tier, so that more of the active dataset resides on and is serviced by the Flash drives. See the FAST VP section. Hybrid pools can have up to 3 tiers (Extreme Performance, Performance, and Capacity). Dell EMC recommends using only a single drive speed, size, and RAID width within each tier of a hybrid pool. EXAMPLE: • For the Extreme Performance tier, use only 800GB SAS Flash 2 drives, and configure them all with RAID-5 8+1. • For the Performance tier, use only 1.2TB SAS 10K RPM drives, and configure them with RAID-5 4+1. • For the Capacity tier, use only 6TB NL-SAS drives, and configure them all with RAID-6 6+2.

GENERAL RECOMMENDATIONS FOR STORAGE POOLS

Unity supports 2 different types of storage pools, traditional pools and dynamic pools. The following recommendations are applicable to both types of pool. In general, it is recommended to use fewer storage pools within Unity, as this reduces complexity and increases flexibility. However, it may be appropriate to configure multiple storage pools, in order to: • Separate workloads with different I/O profiles • Separate pools where FAST Cache is and is not active • Dedicate resources to meet specific performance goals • Separate resources for multi-tenancy • Create smaller failure domains

STORAGE POOL CAPACITY

Storage pool capacity is used for multiple purposes: • To store all data written into storage objects (LUNs, file systems, datastores, and VVols) in that pool • To store data which is needed for Snapshots of storage objects in that pool • To track changes to replicated storage objects in that pool • To perform efficient data relocations for FAST VP Storage pools must maintain free capacity in order to operate properly. By default, Unity will raise an alert if a storage pool has less than 30% free capacity, and will begin to automatically invalidate Snapshots and Replication sessions if the storage pool has less than 5% free capacity. Dell EMC recommends that a storage pool always have at least 10% free capacity.

SYSTEM DRIVES

The first 4 drives of every Unity system are called the system drives (DPE Disk 0 through DPE Disk 3). Unity uses capacity from these 4 drives to store copies of configuration information and other critical system data. Therefore, the available capacity from each of these drives is about 107GB less than from other drives. System drives can be added to storage pools like any other drive, but offer less usable capacity due to the system partitions. To reduce the capacity difference when adding the system drives to a pool, Dell EMC recommends using a smaller RAID width for the tier which will contain the system drives. EXAMPLE: Choose RAID-5 4+1 for a tier containing the system drives, instead of 12+1. Due to the capacity difference of the system drives, Unity will not add them to storage pools until all other non-spare drives of the same type have been used. When used in traditional storage pools, the system drives are counted by Unity in determining how many hot spare drives need to be reserved, but note that unbound system drives cannot be used as hot spare drives. The system drives also service a modest IOPS workload related to system management functions. For systems with Flash system drives, this workload is negligible. Unity Hybrid Flash arrays can use HDD (SAS or NL-SAS) as system drives. When used in a storage pool, these HDD system drives may have a lower performance capability than other HDD drives of the same type. Consider not using the system drives in storage pools for large configurations with high drive counts and many storage objects, if the system drives are HDD.

STORAGE OBJECT TYPES

Unity supports two types of storage objects, thin or thick. By default, Unity creates thin storage objects. Thin storage objects are virtually provisioned and space efficient. In general, Dell EMC recommends using thin storage objects, as they provide the best capacity utilization, and are required for most features. Thin storage objects are recommended when any of the following features will be used: • Data Reduction • Snapshots • Thin Clones • Asynchronous Replication Thick storage objects will reserve capacity from the storage pool, and dedicate it to that particular storage object. Thick storage objects guarantee that all advertised capacity is available for that object. Thick storage objects are not space efficient, and therefore do not support the use of space-efficient features. If it is required to enable a space-efficient feature on a thick storage object, it is recommended to first migrate the thick storage object to a thin storage object, and enable the feature during the migration (for Data Reduction) or after migration has completed (for Snapshots, Thin Clones, and Asynchronous Replication). In addition to capacity for storing data, storage objects also require pool capacity for metadata overhead. The overhead percentage is greater on smaller storage objects. For better capacity utilization, Dell EMC recommends configuring storage objects that are at least 100GB in size, and preferably at least 1TB in size.