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QTS 5.0.x

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Qtier and SSD Cache Comparison


Qtier can be used at the same time as SSD cache.

There are three main configuration options when configuring a NAS with a mixture of HDDs and SSDs.


SSD Usage

HDD Usage

Qtier Storage Pool

Qtier Storage Pool (combined with HDDs)

Qtier Storage Pool (combined with SSDs)

SSD Cache

SSD cache

HDD-only storage pool

All-SSD Storage Pool

SSD-only storage pool

HDD-only storage pool

Table 1. Qtier, SSD Cache, and All-SSD Storage Pool Comparison

Qtier Storage Pool

SSD Cache

All-SSD Storage Pool

Total file storage space

High (SSDs + HDDs)

Moderate (HDDs only)

Low (SSDs only)

Maximum SSD capacity

No limit

Up to 4 TB depending on installed memory

No limit

SSD expansion

Expand as needed

Limited by available memory

Expand as needed

Applicable storage

Thick volumes, thin volumes and block-based LUNs in the pool

All volumes and LUNs on the NAS

Volumes and LUNs created on the SSDs

Data migration

Scheduled or when NAS load is low


No migration required

Data migration method

QTS writes incoming data to the SSD tier and moves data to different tiers based on access frequency.

  • Write cache: QTS writes incoming data to the SSD cache and then flushes the cache to disk periodically.

  • Read cache: QTS copies data to the cache as it is accessed.

No migration required

Recommended use cases

  • Total SSD capacity is high

  • I/O is predictable

  • The storage pool only occasionally experiences periods of intense random I/O access

  • I/O is unpredictable and frequently happens in random bursts

  • Home usage, where the NAS will be used for a large range of different applications

Applications require consistent intensive random read-write access

Usage examples

File server, web server, email servers, basic database services (With Qtier IO Aware)

Video editing, virtualization

Business critical database or other application