Administrator Guide
Only a single read-cache disk group may exist within a pool. Increasing the size of read cache within a pool requires the user to remove the
read-cache disk group, and then re-add a larger read-cache disk group. It is possible to have a read-cache disk group that consists of one
or two disks with a non-fault tolerant RAID level. For more information on read cache, see About SSD read cache.
About RAID levels
The RAID controllers enable you to set up and manage disk groups, the storage for which may be spread across multiple disks. This is
accomplished through firmware resident in the RAID controller. RAID refers to disk groups in which part of the storage capacity may be
used to achieve fault tolerance by storing redundant data. The redundant data enables the system to reconstruct data if a disk in the disk
group fails.
For a description of the ADAPT data protection level, see About ADAPT.
NOTE: Choosing the right RAID level for your application improves performance.
The following tables:
• Provide examples of appropriate RAID levels for different applications.
• Compare the features of different RAID levels.
• Describe the expansion capability for different RAID levels (linear disk groups).
• Suggest the number of disks to select for different RAID levels (virtual disk groups).
• Describe the expansion capability for different RAID levels.
NOTE: To create an NRAID, RAID-0, or RAID-3 (linear-only) disk group, you must use the CLI add disk-group
command. For more information about this command, see the
Dell EMC PowerVault ME4 Series Storage System CLI
Guide
.
NOTE: You can only create RAID-1, RAID-5, RAID-6, and RAID-10 and ADAPT virtual disk groups.
Table 1. Example applications and RAID levels
Application RAID level
Testing multiple operating systems or software development
(where redundancy is not an issue)
NRAID
Fast temporary storage or scratch disks for graphics, page layout,
and image rendering
0
Workgroup servers 1 or 10
Video editing and production 3
Network operating system, databases, high availability applications,
workgroup servers
5
Very large databases, web server, video on demand 50
Mission-critical environments that demand high availability and use
large sequential workloads
6
Environments that need flexible storage and fast rebuilds ADAPT
Table 2. RAID level comparison
RAID level Min. disks Description Strengths Weaknesses
NRAID 1 Non-RAID, nonstriped
mapping to a single disk
Ability to use a single disk
to store additional data
Not protected, lower
performance (not
striped)
0 2 Data striping without
redundancy
Highest performance No data protection: if one
disk fails all data is lost
1 2 Disk mirroring Very high performance
and data protection;
minimal penalty on write
High redundancy cost
overhead: because all
data is duplicated, twice
16 Getting started