More on storage here
Windows Server 2008 and 2008 R2 includes a (DSM) Device Specific Module that works with storage devices that support (ALUA) Asymmetric Logical Unit Access and Active / Active storage controllers. DSM have provided by the SAN vendor and interface with Windows Server MPIO and Storage Manager for SANs. The ALUA model allows the server to see the LUNs over both storage controllers but only one path should be preferred i.e. the one with direct access to the LUN; accessing the LUNs via the non-direct or unoptimised path can cause path thrashing.
Windows Server 2008 and 2008 R2 supports the following MPIO policies:
- Failover – Uses one path for all storage I/O; all other paths are standby paths which are defined as most preferred to least preferred.
- Failback – Uses one path for storage I/O; all other paths are standby paths. When the preferred path becomes available storage I/O is switched.
- Round Robin – All paths are used for storage I/O.
- Round Robin with a subset of paths – A defined set of paths are used for storage I/O with another set of paths defined for standby.
- Dynamic least queue depth – storage I/O uses the path with the smallest outstanding I/O queue.
- Weighted path – All paths are given a weighting, the path with the smallest weighting is used for storage I/O.
Block based storage
Device where raw volumes are created; the filesystem of the block storage is purely determined by the OS utilising the storage e.g. VMware vSphere would format the volume VMFS whereas Windows Server would format the volume NTFS. Access is handled by the operating system.
File based storage
Storage accessed via SMB / CIFS or NFS. The access is handle by the file based storage device.
Windows Server 2008 and 2008 R2 has Storage Manager for SANs and Storage Explorer. The link above has Storage Manager for SANs information. Storage Explorer uses (iSNS) Internet Storage Name Service to discover iSCSI fabric information and SNMP, telnet or http to discover and interface with Fibre Channel fabrics.