RAID
Redundant array of independent disks (RAID) combines multiple physical disks into a single storage unit,
and then distributes data across the disks in one of several predefined methods.
The following features make RAID ideal for use with data storage and NAS applications.
RAID Feature
Description
Advantages
Disadvantages
Grouping
Disks that are combined
using RAID form a RAID
group, which QTS
considers one large
logical disk.
Managing the storage space of
one large disk is simpler and
more efficient than multiple small
disks.
Initial configuration can be
more complicated.
Striping
Data is split into smaller
pieces. Each piece is
stored on a different disk
in the RAID group. QTS
can then access that
data by reading from or
writing to multiple disks
simultaneously,
increasing read and write
speeds.
• Greater read/write speeds,
compared to a single disk
• Speeds can be increased
further by adding disks
If one disk in the RAID
group fails, and the RAID
group has no redundancy,
all data will be lost.
Redundancy
Each disk in the RAID
group can store the
following:
• Complete copy of the
stored data
• Metadata that allows
reconstruction of lost
data
• Disks can fail or be removed
from the RAID group without
any loss of data
• Users can access data while
failed disks are being
replaced
Total storage capacity of
the RAID group is reduced.
RAID Types
QTS supports several RAID types. Each type provides a different combination of performance and
redundancy.
Important
• If disks with different capacities are combined in one RAID group, all disks function
according to the capacity of the smallest disk. For example, if a RAID group contains
five 2 TB disks and one 1 TB disk, QTS detects six 1 TB disks.
QNAP recommends the following when mixing disks of different capacities.
a.
Create a separate RAID group for each capacity.
b.
Combine the RAID groups using storage pools.
• If different types of disk (HDD, SSD, SAS) are combined in one RAID group, the RAID
group will function according to the speed of the slowest disk.
QTS 4.5.x User Guide
Storage & Snapshots
202