Reporting the Space Available in a Disk Array

When you think of the most important thing a SAN administrator does for its internal customers, it comes down to simply allocate some disk space to a server with a certain level of availability (RAID, backups, etc.). This is what everybody in the IT department expects the SAN administrator to do: give them some disk space from a disk array. Surprisingly though, most SAN administrators don’t know how much disk space (at which level of protection) is available in their disk arrays. To be fair, calculating the available disk space in a disk array is not something trivial as the data organization and replication gets more and more complicated and virtualized. No administration interface from the disk array vendors provide a clear report of the available disk space from the unassigned physical disks and the RAID sets.

When monitoring a disk array, Hardware Sentry KM reports the available disk space in the different data layers. This is represented by the UnallocatedSpace parameter of the Logical Disk class.

The Logical Disk class is used to represent different types of disk abstractions in a disk array:

•	Primordial Storage Pool: “virtual” pool grouping all of the physical disks in the disk array. Most of the time, this “primordial storage pool” is not represented in the administration interface of the array vendor.

•

Storage Pool: group of physical disks arranged with a certain level of RAID. Depending on the vendor, the “storage pool” concept may have a different name: “Array” for IBM, “Disk Group” for HP, etc. The “storage pool” denomination is the official SMI-S standard name. Storage pools are allocated from the primordial storage pool or from another storage pool.

•	Volume: part of a storage pool dedicated and made available to a server.

Typically, SAN administrators setup a bunch of storage pools with different levels of protection and availability. Then, then allocate volumes from a specific storage pool depending on the customer needs (redundancy, speed, backups, etc.). Therefore, they need to know, at any time, how much space is available on each storage pool.

Hardware Sentry KM reports the unallocated space of each storage pool in a disk array, including the “primordial storage pool”. The UnallocatedSpace parameter is not available for the logical disk instances representing “Volumes” though, since the amount of space being used by a server in an allocated volume does not fall under the SAN administrator responsibility.

Additionally, under the Capacity Report icon, Hardware Sentry KM reports the total unallocated space in the disk array, as the sum of the “UnallocatedSpace” parameters of all storage pools, including the primordial storage pool. It’s a quick way to see the amount of available disk space in a disk array (UnallocatedDiskSpace), the amount of space online (LogicalDiskSpace, equals to the sum of Volumes), and the total physical disk size (PhysicalDiskSpace).

To get a rapid view of all of this information, right-click the hardware icon representing the disk array > KM Commands > Reporting > Hardware Inventory.