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Dell Unity storage supports two types of storage pools on All-Flash storage systems: traditional pools and dynamic pools. Dynamic pools were introduced in Dell Unity OE version 4.2 for all-flash storage models and became the default pool type in Dell Unisphere. While traditional pools are still supported on all-flash models, they can only be created through the Unisphere CLI or REST API.
Dynamic pools offer many benefits over traditional pools. The new pool structure eliminates the need to add drives in the multiples of the RAID width, allowing for greater flexibility in managing and expanding the pool. Dedicated hot spare drives are also no longer required with dynamic pools. Data space and replacement space are spread across the drives within the pool. Spreading space across drives within the pool provides better drive utilization, improves application I/O, and speeds up the proactive copying of failing drives and the rebuild operation of failed drives.
In general, create dynamic pools with large numbers of drives of the same type and use few storage pools within the Dell Unity system. However, it may be appropriate to configure additional storage pools in the following instances:
Additional information can be found in the documents, Dell Unity: Dynamic Pools and Dell Unity Family Configuring Pools.
Storage pool capacity is used for multiple purposes:
Storage pools must maintain free capacity to operate properly. By default, a Dell Unity system will raise an alert if a storage pool has less than 30% free capacity. If the alert is raised, the system will begin to automatically invalidate snapshots and replication sessions if the storage pool has less than 5% free capacity. Dell Technologies recommends that a storage pool always has at least 10% free capacity.
More drives can be added to a storage pool online. However, to optimize the performance and efficiency of the storage, add drives with the same specification, type, and capacity of the existing drives in the pool. Though not required, add several drives equal to the RAID width + 1, which allows the new capacity to be immediately available. Data is automatically rebalanced in the pool when drives are added.
Note: Once drives are added to a storage pool, they cannot be removed unless the storage pool is deleted.
All-flash pools provide the highest level of performance in Dell Unity systems. Use an all-flash pool when the application requires the highest storage performance at the lowest response time. Note the following considerations with all-flash pools:
For example: For an all-flash pool, use 800 GB SAS flash 3 drives and configure them all with RAID 5 8+1.
Hybrid pools (including a combination of flash drives and hard disk drives) are not supported with Dell Unity All-Flash arrays.