QNAP TVS-472XT 4-Bay NAS Enclosure - Manual (Page 148)

7. Click OK.
Configuring SSD Cache Settings
1. Go to Storage & Snapshots > Storage > Cache Acceleration .
2. Click Manage and then select Settings.
The Switch SSD Cache window opens.
3. 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 .
4. Click Next.
5. 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.
6. Optional: Configure 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.
7. Click Finish.
Cache Missing
If the write-only or read-write cache disks become unavailable because of hardware failure or physical
removal from the NAS, all volumes using the write-cache will also become unavailable and will have Cache
Missing as their status. QTS restricts access to these volumes to protect data integrity, as some volume
data may be stored in the write cache without being flushed to disk.
When the SSD cache is missing, restore it using one of the following methods:
• If the SSD cache disks were removed from the NAS, re-insert the disks into the same drive bays.
• Resolve any RAID errors.
• Restart the NAS.
QTS 4.4.x User Guide
Storage & Snapshots 147