Volume Type
Static Thick Thin
Read/write speed Fastest for random writes Good Good
Flexibility Inflexible
A volume can only be
expanded by adding
extra drives to the NAS.
Flexible
A volume can easily be
resized.
Very flexible
A volume can be resized.
Also unused space can
be reclaimed and added
back into the parent
storage pool.
Parent storage space RAID group Storage pool Storage pool
Volumes allowed in
parent storage space
One One or more One or more
Initial size Size of the parent RAID
group
User-specified Zero
Storage pool space is
allocated on-demand, as
data is written to the
volume. This is called
thin provisioning.
Maximum size Size of the parent RAID
group
Size of the parent
storage pool
Twenty times the amount
of free space in the
parent storage pool
The size of a thin volume
can be greater than that
of its parent storage pool.
This is called over-
allocation.
Effect of data deletion Space is freed in the
volume
Space is freed in the
volume
QTS can reclaim the
space and add it back
into the parent storage
pool.
Method of adding storage
space
• Add disks to the NAS
• Replace existing
disks with higher
capacity disks
Allocate more space from
the parent storage pool
Allocate more space from
the parent storage pool
Snapshot support (fast
backup and recovery)
No Yes Yes
Qtier (automatic data
tiering) support
No Yes Yes
Legacy Volumes
A legacy volume is a volume created in QTS 3.x or earlier, before QTS had storage pools. A NAS will contain
legacy volumes in the following situations:
• A volume was created on a NAS running QTS 3.x or earlier, and then the NAS was updated to QTS 4.0
or later.
• A volume was created on a NAS running QTS 3.x or earlier, and then the disks containing the volume
were moved to a different NAS running QTS 4.0 or later.
You can use legacy volumes for data storage, but their behavior and status will not be consistent with other
volume types. They also cannot use newer QTS features such as snapshots.
QTS 4.5.x User Guide
Storage & Snapshots 180
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