Developers Guide

6 Understanding RAID with Dell SC Series Storage | 3104-CD-DS
1 SC Series storage basics
SC Series arrays include redundant, hot-swappable components (for example, physical disks, control
modules, fans, and power supplies) for a no-single-point-of-failure configuration. Along with redundant
hardware, several different RAID levels are supported with each configuration optimized to maximize
performance, availability, and capacity of the SC Series architecture.
1.1 Tiers
When configured, all SC Series disks act as a single pool of storage virtualizing the RAID configurations, disk
types, and speed. The disks are grouped by speed into as many as three tiers. Each tier is determined by the
speed of the disk from the fastest (Tier 1) to slowest disk (Tier 3).
Table 1 shows each disk type and the typical tiers assigned to those disk based on speed. However, many
variations of tiering are possible and not all combinations are included.
Example disk types and typical associated tiers
Disk type
Typical tier
Notes
SSD–write intensive
(SSD-WI)
Tier 1
Provides best performance
SSD–read intensive
(SSD-RI)
Tier 2
Provides good read and write performance.
Use in Tier 1 in absence of SSD-WI.
SSD (other types)
Tier 1
Use when SSD-WI are absent.
Otherwise, use in any tier.
15K HDD
Tier 1
Use when SSDs are absent.
Otherwise, use in Tier 2 or Tier 3.
10K HDD
Tier 2
May also be used in Tier 1 if faster HDDs or SSDs are not
available.
Tier 3 is also appropriate in some cases.
7.2K HDD
Tier 3
Only used in Tier 1 when these are the only disk types available.
In cases where more than three speeds of disks are present, the third tier contains the lowest-speed disks.
These disk types are just an example of the disks available today and may evolve over time.
Note: RAID tiering for the Dell Storage SCv2000 Series controllers moves data between RAID levels within
a tier. No movement of data occurs between tiers on different disks.
1.2 RAID redundancy
In most configurations, all disks form a single pool of storage in a managed disk folder. Storage Center OS
software defines the RAID protection for the disk pool. RAID redundancy levels provide fault tolerance for a
disk failure. Redundancy options may be restricted depending on the disk size.