ScaleIO Basic Concepts for vSphere

SDC  – ScaleIO Data Client 
Vib or Driver that exposes ScaleIO block volumes to the application . EG ESX. It allows the hypervisor to issue IO request to the ScaleIO Storage array. SDC communicate with neighbour nodes over TCP/IP and is fully routable. On an ESX Host the SDC is installed on the Physical host by the vSphere Webclient once the ScaleIO plugin  has been registered via a powercli script that is included in the ScaleIO firmware download from EMC. A reboot is required to compete the install.
;sdc

SVM – ScaleiO Virtual Machine 
Once the SDC has been installed your can the deploy the SVM on to each SDS. The SVM is deploy from an OVF template which can be imported via the same PowerCli script that integrates the ScaleIO Plugin to vCenter. There is also a manual process for deploying. Each SVM contains a number of different components and perform several different roles.

SDS – ScaleIO Data Server
SDS interacts with the hosts volume manager. It owns the local storage that contributes to the overall storage solution. The SDS performs back end I/O operations as requested by the SDC.
sds

MDM – MetaData Manager 
Configures and monitors the ScaleIO system. It  holds Metadata such as device mapping, snapshots, remaining capacity etc. MDMs are configured in Primary, Secondary and Tie Breaker mode.  For a Five node cluster you can configure 1 Primary , Two Slaves and Two Tiebreakers. Tie Breakers are used in the event of split brain scenarios. MDMs collect all tracked changes on each SDS in the event of a rebuild of data manages the process. In the event of a SDS outage the MDM initiates a rebuild  of the data on the remaining SDS nodes when it does not receive a heart beat from the downed SDS node.
mdm

LIA – Light Install Agent
Is installed on all ScaleIO SVM’s creates a trusts with the installation Manager and nodes to allow install, upgrade and uninstalls to take place.

Gateway 
Is created from the same template as the SVM. The Rest API resides on this VM. The Gateway communicates to the Primary MDM and presents its answer is a RESTful manner. All scli  (Scale I/O Command Line interface)  commands are also available via the Gateway API. For VxRack – Vision Intelligent Software gathers data analysis and system helth from the ScaleIO nodes via the RESTAPI

IM – Install Manager
Preforms systems checks prior to completing installs, upgrades and uninstall operations.

Protection Domains
Allows you to separate physical nodes and can all you to cater for multitenancy with an over all solution. Nodes can only belong to one PD. Mixed nodes types are permissible within PDs

Storage Pools 
Where PD are utilized to separate physical node, SP can be used to separate or mix disk types. Allowing you to create a storage profiles based on performance, tiering and or to ensure end users SLAs are met.  An E.G examples of Storage Pool would be Flash only which would allow for best performance or SAS which would be lower cost and higher capacity. A Node can divide its disk to separate  pools along as the node and pool are located in the same  protection domain.

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