SAN Volume Controller overview
The SAN Volume Controller system combines software and hardware into a comprehensive, modular appliance that provides symmetric virtualization.
Symmetric virtualization is achieved by creating a pool of managed disks (MDisks) from the attached storage systems and optional SAS expansion enclosures.Volumes can be created in a pool for use by attached host systems. System administrators can view and access a common pool of storage on the storage area network (SAN). or local area network (LAN). This functionality helps administrators to use storage resources more efficiently and provides a common base for advanced functions.
A SAN is a high-speed Fibre Channel network that connects host systems and storage devices. A LAN is a high-speed Ethernet network that connects host systems and storage devices. In a SAN and LAN, a host system can be connected to a storage device across the network. The connections are made through units such as routers and switches. The area of the network that contains these units is known as the fabric of the network.
IBM Spectrum Virtualize software
IBM® SAN Volume Controller system is built with IBM Spectrum Virtualize™ software , which is part of the IBM Spectrum Storage™ family.
http://www.ibm.com/systems/storage/spectrum
Volumes
System nodes present volumes to the hosts. Most of the advanced system functions are defined on volumes. These volumes are created from managed disks (MDisks) that are presented by the RAID storage systems. The volumes can also be created by arrays that are provided by flash drives in an expansion enclosure. All data transfer occurs through the system node, which is described as symmetric virtualization.
Figure 2 shows the data flow across the fabric.
The nodes in a system are arranged into pairs that are known as I/O groups. A single pair is responsible for serving I/O on a volume. Because a volume is served by two nodes, no loss of availability occurs if one node fails or is taken offline. The Asymmetric Logical Unit Access (ALUA) features of SCSI are used to disable the I/O for a node before it is taken offline or when a volume cannot be accessed via that node.
Volume types
- Basic volumes, where a single copy of the volume is cached in one I/O group. Basic
volumes can be established in any system topology; however, Figure 3 shows a standard system
topology.Figure 3. Example of a basic volume
- Mirrored volumes, where copies of the volume can either be in the same storage pool
or in different storage pools. As Figure 4 shows, the
volume is cached in a single I/O group. Typically, mirrored volumes are established in a standard
system topology.Figure 4. Example of mirrored volumes
- Stretched volumes, where copies of a single volume are in different
storage pools at different sites. As Figure 5 shows, the volume is cached in one I/O group. Stretched volumes are only available in stretched
topology systems.Figure 5. Example of stretched volumes
- HyperSwap volumes,
where copies of a single volume are in different storage pools that are on different sites. The
volume is cached in two I/O groups that are on different sites, as Figure 6 shows. These volumes can be created only
when the system topology is HyperSwap.Figure 6. Example of HyperSwap volumes
System topology
- Standard topology, where all nodes in the
system are at the same site.
Figure 7. Example of a standard system topology
- Stretched topology, where each node of
an I/O group is at a different site. When one site is not available, access to a volume can continue
but with reduced performance. Figure 8. Example of a stretched system topology
- HyperSwap topology, where the system consists of at least two I/O
groups. Each I/O group is at a different site. Both nodes of an I/O group are at the same site. A
volume can be active on two I/O groups so that it can immediately be accessed by the other site when
a site is not available. Figure 9. Example of a HyperSwap system topology
Summary of system topology and volumes
Table 1 summarizes the types of volumes that can be associated with each system topology.
| Topology | Volume Type | ||||
|---|---|---|---|---|---|
| Basic | Mirrored | Stretched | HyperSwap | Custom | |
| Standard | X | X | X | ||
| Stretched | X | X | X | ||
| HyperSwap | X | X | X | ||
System management
A system is composed of individual nodes that present a single point of control for system management and service. System management and error reporting are provided through an Ethernet interface to one of the nodes in the system, which is called the configuration node. The configuration node runs a web server and provides a command-line interface (CLI). Any node in the system can be the configuration node. If the current configuration node fails, a new configuration node is selected from the remaining nodes. Each node also provides a command-line interface and web interface for initiating hardware service actions.
Fabric types
I/O operations between hosts and system nodes and between the nodes and arrays use the SCSI standard. The nodes communicate with each other through private SCSI commands.
All nodes that run system software version 6.4 or later can support Fibre Channel over Ethernet (FCoE) connectivity.
Table 2 shows the fabric type that can be used for communicating between hosts, nodes, and RAID storage systems. These fabric types can be used at the same time.
| Communications type | Host to system nodes | System nodes to storage system | System nodes to system nodes |
|---|---|---|---|
| Fibre Channel SAN | Yes | Yes | Yes |
iSCSI
|
Yes | Yes | No |
| Fibre Channel Over Ethernet SAN (10 Gbps Ethernet) | Yes | Yes | Yes |
Flash drives
Some system nodes are attached to expansion enclosures that contain flash drives. These flash drives can be used to create RAID-managed disks (MDisks) that in turn can be used to create volumes. Flash drives are in an expansion enclosure that is connected to both sides of an I/O group.
Flash drives provide host servers with a pool of high-performance storage for critical applications. MDisks on flash drives can also be placed in a storage pool with MDisks from regular RAID storage systems. IBM Easy Tier performs automatic data placement within that storage pool by moving high-activity data onto better-performing storage.
SAN Volume Controller nodes
Each node is an individual server in a SAN Volume Controller clustered system on which the SAN Volume Controller software runs.
The nodes are always installed in pairs; a minimum of one pair and a maximum of four pairs of nodes constitute a system. Each pair of nodes is known as an I/O group.
I/O groups take the storage that is presented to the SAN by the storage systems as MDisks and transforms the storage into logical disks (volumes) that are used by applications on the hosts. A node is in only one I/O group and provides access to the volumes in that I/O group.
SAN Volume Controller 2145-SV1 node features
The SAN Volume Controller 2145-SV1 system has the following features.
SAN Volume Controller 2147-SV1 node features
The SAN Volume Controller 2147-SV1 system includes all of the features of the SAN Volume Controller 2145-SV1 system plus Enterprise Class Support and a three-year warranty.
SAN Volume Controller 2145-DH8 node features
The SAN Volume Controller 2145-DH8 node has the following features: