Cache; Caching Modes - Dell EMC VxFlex Ready Node User Manual
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Architecture
Cache
Mode
RAM Read Cache
(RMcache)
Read Flash Cache
(RFcache)
Dell EMC VxFlex Ready Node AMS User Guide
38
Clone Status: unsupported This means that Clone Block/Full Copy/Xcopy is
not supported.
Zero Status: supported This means that write same is supported.
Delete Status: supported This means that UNMAP is supported.
Note:
Thin provisioning is not shown in VAAI output.
VxFlex OS offers a number of caching options, for the purpose of enhancing system
performance.
The following caching options are supported by VxFlex OS:
RAM Read Cache (using DRAM server memory)
l
Read Flash Cache (using SSD and NVMe SSD devices)
l
In addition, the following caching solution is available, in VxFlex Ready Node systems
only:
DAS Cache (using SSD devices)
l
Note:
For the most updated list, see the DAS Cache support matrix at
topics-cdn.dell.com/pdf/dell-sandisk-das-cache_Reference-Guide_en-us.pdf.
SSDs used for caching cannot be used for storage purposes.
Note:
If CacheCade or DAS Cache is used, you must configure External
acceleration. Some devices are already benefitting from an external (For example,
a non-VxFlex OS related) acceleration/caching mechanism. This input is required
in order to avoid alerts about media type mismatches. For example, when the user
adds an HDD device which the SDS perceives as being too fast to fit the HDD
criteria.
Read Flash Cache (RFcache) and DAS Cache cannot be used simultaneously in the
same Storage Pool. However, a node can contain devices using different caching
types, as long as the corresponding devices are allocated to different dedicated
Storage Pools (one Storage Pool using DAS Cache, and another using Read Flash
Cache.
The following table summarizes information about the caching modes provided by the
system.
Table 3 Caching modes
Description
Considerations
Read-only caching
RAM Read cache, the fastest type of caching,
performed by server
uses RAM that is allocated for caching. Its size is
RAM.
limited to the amount of allocated RAM.
Read-only caching
RFcache uses the full capacity of SSD devices
performed by one or
(up to eight) to provide a larger footprint of
more dedicated SSD or
read-only LRU (Least Recently Used) based-
Note:
The amount that may be allocated is limited,
and can never be the maximum available
RAM.
https://
Default Setting
Disabled, except when
storage-only nodes are
deployed.
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