About Network Managed Volume (NMV) Pools
NMV pools are comprised of a collection of disks— even of different kinds— from JBOD (just a bunch of disks) enclosures to intelligent storage arrays. NMV pools allow all your available physical storage to be pooled and then allocated from the pools as needed. Any number of pools can be created. See Preparing Disks for NMV Pools.
SANmelody software enables administrators to centrally manage pooled storage resources. NMV pools can also eliminate the need for administrators to monitor usage on each client machine to determine when they are likely to run out of disk space and avoid conventional disk resizing outages. When a pool nears depletion, additional physical disks can be added to the pool non-disruptively and capacity growth occurs transparently to the client.
NMVs are extended virtual devices where the total capacity presented to application servers may exceed the physical resources in the NMV pool of storage. NMVs allow LUNs, up to a maximum size of one petabyte (PB), to be presented to the host without requiring corresponding storage assets. In other words, this extended “virtual” volume no longer has a one-to-one relationship with the storage resources physically allocated to it. Because adding more physical storage assets to the storage server can expand the storage in the pool, there is almost no limit on the size of a single NMV pool. Each storage server can support multiple NMV pools allowing large amounts of storage to be centrally managed in this way.
The size of Storage Allocation Units (SAU) in a pool is set when the pool is created and cannot be changed. SAUs can range in size from 1 MB to 2048 MB (in powers of 2). The default is 128 MB. A 128 MB SAU size can safely handle pools containing up to 1000 TB of storage resources. If you intend on adding more than 1000 TB of storage to the pool, you should increase the SAU size accordingly.
NMVs are the basis of what we refer to as virtual volumes and are ultimately served to application servers as storage resources. The size of the virtual volume must be a multiple of the NMV SAU size. Creating virtual volumes from pools of the same size SAUs allows for greater optimization.
SANmelody software will request more physical storage resources as needed. You will be notified of the pending need for more storage resources via alarms and event log messages. When the NMV pool depletes, you will get a warning message that the pool is reaching the low watermark and you will not be able to add more NMVs. You must then add more unpartitioned and unallocated physical disks. If you fail to do this, you will next see another error message informing you that a new storage unit failed to allocate because the NMV pool is empty. As with traditional storage, application servers will not be able to write additional data to the LUN until new disks are added to the pool.
Operating systems may have limitations on how they work with NMVs. You can modify the NMV logical size if necessary.
Refer to our Technical Support Web site for information concerning specific operating systems.