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NAS 202

Using SSD Caching on your ASUSTOR NAS

Learn how to speed up your NAS by using SSD caching.




Upon completion of this course you should be able to:

Set up SSD caching to speed up your NAS.


Course Prerequisites:


Students are expected to have a working knowledge of:





1. Introducing SSD Caching?
2. Setting Up SSD Caching
3. Removing SSD Caching
4. Notes



1. Introducing SSD Caching

SSD caching has two modes: Read/Write and Read-Only. If using one SSD, then Read Only mode is the only option. Read/Write mode is available in addition to the former if two or more SSDs are installed.

Different modes will be automatically created into corresponding RAID configurations according to the number of SSDs. In Read-Only mode, RAID 0 will be created automatically with more than two SSDs. In Read/Write mode, two SSDs will be set to RAID 1, three SSDs will create RAID 5, and four SSDs will set up RAID 10 for caching.

Capacities vary with the RAID level used. RAID 0 combines the capacity of all drives. RAID 1 uses half of the available capacity for storage while the other half is a mirror. RAID 5 uses all but one drive’s worth of capacity.

Read Only mode:
Your NAS will take frequently accessed data and copy it to installed SSDs. When requested data is found to have a copy in installed SSDs, ADM will take advantage of the increased speed of the SSDs to upload data at an accelerated rate.
If requested data is not found in installed SSDs, then the request falls back to installed drives, which are usually slower than SSDs. Requested data will also be copied to the SSDs for increased performance upon future requests. 
If cache drives are full, the oldest data of a comparable size is replaced with recently-requested data.

Read/Write mode:
Reading from read/write mode is identical to read mode. 
Read/write mode adds the ability to write data directly to SSDs from a client. Since SSDs are faster than hard drives, write performance to a NAS with read/write SSD caching enabled is usually higher.
If cache drives are full, the oldest data that has not been accessed will be moved back to the hard drives. 
SSD caching has a number of applications where its advantages can most easily be taken advantage of.
Read Only mode is most suitable for reading of small files that are not frequently modified, like documents provided for sharing and downloading or sharing photos to multiple people.
Read/Write mode is most suitable for small files that are frequently modified, like audio, video and photo editing as well as web server maintenance.
SSD caching has no significant acceleration effect on video file playback and music file streaming.
Note: Small files are files smaller than 1 MB.


2. Setting Up SSD Caching

Please check below items before setting

1. ASUSTOR supports SSD caching on a variety of models. The AS31, 32, 50, 51, 52, 53, 54, 61, 62, 63, 64, 65, 66, 67, 70 and 71 series support SSD caching using SATA SSDs. Models with M.2 slots support SSD caching using M.2 SSDs in addition to SATA SSD caching. These include, but are not limited to the Lockerstor series and Lockerstor Pro series of NAS.  

2. Partitioning of the SSDs for use as both storage and caching is not supported.

One SSD cache can only be used for one volume.

Step 1

If using M.2 SSDs, please shut down NAS first and install your SSDs. SATA SSDs may be installed while the NAS is powered on. Boot the NAS and open Storage Manager. Select and click on the volume that is to be accelerated. Click Management and then click SSD Caching.

Step 2

Select an SSD caching mode. 

Step 3 

Select one or more SSDs

Step 4

Verify and confirm settings.

After an accelerated drive is created, the icon for a volume will change to reflect its status. SSDs that are part of an accelerated drive must be safely removed before removing them from a NAS or performing other types of maintenance, like a RAID upgrade or capacity upgrade.

Click SSD Caching under Management to view cache usage and read hit rate. The higher the hit rate, the higher the efficiency.

3. Removing SSD Caching

Some forms of maintenance require an SSD cache drive to be removed. If migrating to a new NAS, upgrading RAID levels, upgrading capacity, or simply no longer in need of SSD caching you will need to safely remove the SSD cache.

Inside Storage Manager, click a volume, click Management and open SSD Caching.

To remove SSDs from an accelerated volume, click Safely Remove SSD Cache. Your NAS cannot be powered off while SSDs are being safely removed. If your NAS powers off or otherwise is interrupted, it is possible for data loss to occur. After completion, you may remove SATA SSDs or power down the NAS to remove M.2 SSDs.



4. Notes

1. Please refer to your quick installation guide for M.2 SSD installation or view our M.2 SSD installation video here: https://www.youtube.com/watch?v=LhdtX9QCIZQ


2. Every Gigabyte of SSD caching requires approximately 512 KB of system memory. To ensure system stability, ADM will only allow a quarter of total memory to be allocated to SSD caching. ADM automatically reserves memory space based on cache size as well as available RAM.


Listed below are the RAM capacity requirements for various sizes of SSD cache drives on an ASUSTOR NAS device. For example, if you want to use a cache size of 4 TB for caching on a Lockerstor 4 Gen2, it will requires 1820 MB of RAM. RAM used for SSD cache may only occupy up to a quarter of total memory capacity, which means the minimum required total RAM size is 8 GB. This also means that the aforementioned Lockerstor 4 Gen2, which comes with 4 GB of memory as standard, needs to be upgraded to 8 GB to use the full 4 TB SSD cache. 

SSD cache size

Minimum RAM Capacity

Total RAM Usage by SSD Caching






910 MB



1820 MB



3640 MB



7280 MB



14560 MB



29120 MB

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