Creating the SSD Cache

Go to Storage & Snapshots > Storage > Cache Acceleration.

Click

.

The Create SSD Cache window opens.

Click Next.

Select one or more SSDs.

Warning:

All data on the selected disks will be deleted.

Select a cache type.

Cache Type	Description
Read-only	When data is read from a LUN or volume, QTS copies the data to the SSD cache to speed up future read requests.
Write-only	QTS writes incoming data to the SSD cache first, then flushes the data to regular storage later. Read access to the new data is also accelerated while it is in the cache.
Read-write	QTS uses the SSD cache for both read and write caching, accelerating both read and write speeds.

Select a RAID type.

Warning:

Selecting a RAID type with no disk failure protection (Single, JBOD, RAID 0) when the cache type is Write-only or Read-write may result in data loss.

Tip:

RAID 10 provides the best write cache performance.

Click Next.

Optional: Configure SSD over-provisioning.

Over-provisioning reserves a percentage of SSD storage space on each disk in the RAID group to improve write performance and extend the disk's lifespan. You can decrease the amount of space reserved for over-provisioning after QTS has created the RAID group.

Tip:

To determine the optimal amount of over-provisioning for your SSDs, download and run SSD Profiling Tool from App Center.

For details, see SSD Profiling Tool.

Select a cache mode.

Cache Mode	Description	Recommended Use Cases
Random I/O	Only small data blocks are added to the SSD cache. Larger blocks are accessed directly from regular storage.	Virtualization, databases
All I/O	Small and large data blocks are added to the SSD cache. Both sequential and random I/O requests are accelerated.	Video streaming, large file access operations

Tip:

An HDD RAID group may outperform a SSD RAID group for sequential I/O if the ratio of HDDs to SSDs is 3:1 or greater, and the HDD group has a RAID type of RAID 0, 5, 6, or 10. However, SSDs will always be faster for random I/O. If the NAS contains a RAID group of type RAID 0, 5, 6, or 10 that contains three times more disks than the SSD cache, you should select Random I/O.

Optional: Configure the following advanced settings.

Setting	Description
Bypass block size	This value determines the maximum size of the data blocks that are stored in the SSD cache. Selecting a larger size may improve the cache's hit rate but uses more cache space. The default value is 1 MB.
Cache replacement policy	Specify how data is removed from the SSD cache. Choose one of the following options: Least recently used (LRU): Better cache performance but uses more CPU resources. This is the default option. First in first out (FIFO): Lower CPU usage than LRU but might cause worse cache performance.

Setting

Description

Bypass block size

This value determines the maximum size of the data blocks that are stored in the SSD cache. Selecting a larger size may improve the cache's hit rate but uses more cache space. The default value is 1 MB.

Cache replacement policy

Specify how data is removed from the SSD cache. Choose one of the following options:

Least recently used (LRU): Better cache performance but uses more CPU resources. This is the default option.
First in first out (FIFO): Lower CPU usage than LRU but might cause worse cache performance.

Click Next.

Select which volumes and LUNs can use the SSD cache.

Important:

For data safety, volumes and LUNs created on an external storage device cannot use the SSD cache if the cache type is Read-write.

Click Next.

Click Create.

A confirmation message appears.

Select I understand and then click OK.