Administrator 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.)
Redundancy Requirements
Drive size is used to determine the redundancy level to apply to a tier of drives. If any drive in a tier surpasses a threshold size,
a specific redundancy level can be applied to the tier containing that drive. If a redundancy level is required, the Storage Center
operating system sets the level and it cannot be changed.
Table 3. HDD Redundancy Recommendations and Requirements
Disk Size Level of Redundancy Recommended or Enforced
Up to 3 TB Dual redundant is the recommended level
NOTE: Non-redundant storage is not an option for SCv2000 Series storage systems.
3 TB and higher Dual redundant is required and enforced
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