Architecture
SVC is always deployed as a cluster of nodes. Each node is a 1U high rack-mounted appliance based on an IBM System x server, protected by redundant power supplies and an integrated 1U high uninterruptible power supply. The server reports as machine type 2145. Each node has four Fibre Channel ports and two or four 10/1 Gbps Ethernet ports for FCoE, iSCSI and management. Each node runs a Linux kernel and a specialized Virtualization Storage Software environment, that provides proprietary clustering capability. A service controller on each node provides a two-row display and five-button keyboard to configure, service, and monitor node status.
The SVC is a gateway device, meaning it sits between the hosts and the storage arrays, presenting itself to hosts as the target and presenting itself to arrays as the initiator. All Fibre Channel & FCoE ports on the SVC are both targets and initators, whereas iSCSI ports are targets only. Fibre Channel ports on all nodes MUST be zoned together to allow communication between the nodes and the transfer and mirroring of data.
An SVC cluster consists of several pairs of nodes (up to 4 pairs). Each pair of nodes is called an I/O group and provides write data cache mirroring across the pair. In case of I/O path failure, non-disruptive failover is performed inside an I/O group, via multipath drivers such as IBM Subsystem Device Driver (SDD) software or standard MPIO drivers.
Volumes (virtual server LUNs) can be transferred from one I/O group to another non-disruptively. They can also be accessed through any SVC node in case of partial loss of access, called I/O forwarding. In normal operation, volumes are managed by one I/O group at a time to limit the number of write cache mirrored copies.
SVC is based on COMmodity PArts Storage System (Compass) architecture, developed at the IBM Almaden Research Center. The majority of the software has been developed at the IBM Hursley Labs in the UK.
Read more about this topic: IBM SAN Volume Controller
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