Dell Storage Manager 2020 R1 Administrator's Guide

Disk Types

The type of disks present in a Storage Center determines how Data Progression moves data between tiers. Storage Center supports write-intensive SSDs, and 7K, 10K, and 15K HDDs. A minimum number of disks are required, which may be installed in the controller or in an expansion enclosure:

• An all-flash array requires a minimum of four SSDs of the same disk class, for example four write-intensive SSDs.
• A hybrid array requires a minimum of seven HDDs or four SSDs of the same disk class, for example seven 10K HDDs.

Datapage Size

By default, data is migrated between tiers and RAID levels in 2 MB blocks. Data can be moved in smaller or larger blocks to meet specific application requirements. These blocks are referred to as datapages.

• 2 MB – Default datapage size, this selection is appropriate for most applications.
• 512 KB – Appropriate for applications with high performance needs, or in environments in which snapshots are taken frequently under heavy I/O. Selecting this size increases overhead and reduces the maximum available space in the storage type. All-flash storage systems use 512 KB by default.
• 4 MB – Appropriate for systems that use a large amount of disk space with infrequent snapshots.
  CAUTION:Before changing the datapage setting, contact technical support to discuss the impact on performance and for advice about how to ensure that system resources remain balanced.

Redundancy

Redundancy provides fault tolerance for a drive failure. Two redundancy options are available.

• Redundant: Protects against the loss of any one drive (if single redundant) or any two drives (if dual redundant).
• Non-Redundant: Uses RAID 0 in all classes, in all tiers. Data is striped but provides no redundancy. If one drive fails, all data is lost.
  NOTE:Non-Redundant is not recommended because data is not protected against a drive failure. Do not use non-redundant storage for a volume unless the data has been backed up elsewhere.

Redundancy levels per tier include single or dual redundant. The options may be restricted depending on the disk size.

• Single Redundant: Single-redundant tiers can contain any of the following types of RAID storage:
  • RAID 10 (each drive is mirrored)
  • RAID 5-5 (striped across 5 drives)
  • RAID 5-9 (striped across 9 drives)

• Dual redundant: Dual redundant is the recommended redundancy level for all tiers. It is enforced for 3 TB HDDs and higher and for 18 TB SSDs and higher. Dual-redundant tiers can contain any of the following types of RAID storage:
  • RAID 10 Dual-Mirror (data is written simultaneously to three separate drives)
  • RAID 6-6 (4 data segments, 2 parity segments for each stripe)
  • RAID 6-10 (8 data segments, 2 parity segments for each stripe.)