GLOSSARY
A
Active Directory Active Directory (AD) provides directory-based identity-related services. It maintains a
directory that is used to centrally store identity information and security principles, and
uses them to authenticate and authorize users and devices.
Active Forward Rebuild A copy of stored data is currently being rebuilt on another server, due to planned or
unplanned shutdown of a server.
B
Backward Rebuild Data is rebuilt on servers that went offline and became active again. Forward rebuilds
can take a long time, and therefore, it can be quicker to restore and update the data on
a server which has come back online, than it is to do an entire rebuild on a different
server.
Brick A chassis container supplying disk, power and cooling services to a node.
BWC Bandwidth counters.
C
Cache Cache is random access electronic storage used to retain frequently used data for
faster access by the channel. Cache is a critical aspect of storage performance. VxFlex
OS uses server DRAM for Read RAM Cache (RMcache), as well as SSD/Flash devices
(RFcache) for caching reads. VxFlex OS cache uses recently-accessed (LRU) data
readily available to manage caching. I/Os read from cache have a lower response time
than I/Os serviced by the drives. In addition, cached I/Os reduce the data drive
workload, which in many cases is a performance bottleneck in the system.
CacheCade Read and Write caching of storage devices performed by one or more designated SSD
devices in the VxRack Node 100 Series system.
Cache Hit Rate The percentage of I/Os from cache.
Cache Skip Data is written directly to storage, bypassing the cache. Reasons for cache skips
include: I/Os were too large, the cache device was busy, or I/Os were unaligned. The
cache can also be configured to always work in passthrough mode.
Cache Writes Handling
Mode
The caching write-mode used by the system: passthrough mode (writes to storage
only), or cached mode (by default, writes both to cache and to storage).
Cluster Mode VxFlex OS is controlled by a cluster of MDM nodes, minimally consisting of a Master
MDM, Slave MDM, and a Tie Breaker node. 5-node clusters consist of one Master
MDM, two Slave MDMs, and two Tie Breakers.
Dell EMC VxFlex Ready Node AMS User Guide 349
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