Dell PowerFlex Appliance with PowerFlex 4.x Architecture Overview

Protection domains

A protection domain (PD) is a group of nodes or storage data servers that provide data isolation, security, and performance benefits. A node participates in only one protection domain at a time. Only nodes in the same protection domain can affect each other, nodes outside the protection domain are isolated. Secure multi-tenancy can be created with protection domains since data does not mingle across protection domains. You can create different protection domains for different node types with unequal performance profiles. All the hosts in the domain must have the same type and configuration. A PowerFlex hyperconverged node should not be in the same protection domain as a PowerFlex storage-only node. The node configuration must match, which includes the drives, CPU, and memory. Any difference in the node configuration leads to an unknown performance impact.

Storage pools

Storage pools are a subset of physical storage devices in a protection domain. Each storage device belongs to one (and only one) storage pool. The best practice is to have the same type of storage devices (HDD versus SSD or SSD versus NVMe) within a storage pool to ensure that the volumes are distributed over the same type of storage within the protection domain.

PowerFlex supports two types of storage pools. You can choose between both layouts. A system can support both fine granularity (FG) and medium granularity (MG) pools on the same storage data server nodes. Volumes can be non-disruptively migrated between the two layouts. Within an fine granularity pool, you can enable or disable compression on a per-volume basis:

• Medium granularity: Volumes are divided into 1MB allocation units, distributed, and replicated across all disks contributing to a pool. MG storage pools support either thick or thin-provisioned volumes, and no attempt is made to reduce the size of user-data written to disk (except with all-zero data). MG storage pools have higher storage access performance than fine granularity storage pools but use more disk space.
• Fine granularity: A space efficient layout, with an allocation unit of just 4 KB and a physical data placement scheme based on log structure array (LSA) architecture. Fine granularity layout requires both flash media (SSD or NVMe) as well as SDPM or NVDIMM to create an fine granularity storage pool. fine granularity layout is thin-provisioned and zero-padded by nature, and enables PowerFlex to support in-line compression, more efficient snapshots, and persistent checksums. Fine granularity storage pools use less disk space than medium granularity storage pools but have slightly lower storage access performance.

Fault sets

A fault set is a logical entity that contains a group of storage data servers within a protection domain that have a higher chance of going down together; for example, if they are all powered in the same rack. By grouping them into a fault set, PowerFlex mirrors data for a fault set on storage data servers that are outside the fault set. Thus, availability is assured even if all the servers within one fault set fail simultaneously.