Dell EMC VxFlex Ready Node, User Manual

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Table 3 Caching modes (continued)
Mode Description Considerations Default Setting
NVMe SSD devices in
the server. caching resources for the SDS. This type of
caching reacts quickly to workload changes to
speed up HDD Read performance.
Several SSD devices can be allocated to a shared
cache pool, and therefore the cache size is
limited in size only by the amount of SSDs
allocated for this purpose.
The RFcache driver must be installed during
deployment. Caching devices can be defined
either during the installation process or after
deployment.
Limitations:
RFcache does not support partitions on devices
installed on Windows nodes.
Support matrix:
l
An RFcache device (flash device) can be
partitioned only on Linux.
l
An SDS storage/source device cannot be
partitioned if it needs to be accelerated by
RFcache.
l
An SDS storage/source device as a file (over
file system), cannot be accelerated by
RFcache.
l
CloudLink Data at Rest Encryption (D@RE)
is not supported on devices used for the
RFcache feature.
DAS Cache Read and write-back
caching performed by
one or more dedicated
SSD devices in the
server DAS Cache uses the full capacity of one or more
SSD devices to provide a large footprint of both
read and write-back caching resources to the
SDS. This caching mode moves "hot" (active)
chunks of data from HDDs to cache, for Read
and Write buffering. For write-back caching, the
write is temporarily written to the SSD, which is
much faster than an HDD, allowing faster
response of the SDS to write acknowledgment.
One SSD device can accelerate several HDDs (in
DAS Cache they are called "Volumes"). Striping
the Cache on two devices is not supported in the
VxFlex Ready Node solution.
CloudLink Data at Rest Encryption (D@RE) is
not supported on devices used for the DAS
Cache feature.
Note: If a fault occurs in the caching device
before the writes have been offloaded, all the
HDD devices cached by DAS Cache acquire
failed status, and a rebuild process
Disabled
Architecture
Dell EMC VxFlex Ready Node AMS User Guide 39