ISCSI storage virtualization?

Storage virtualization
A reader asks: Happy with a new purchase but I'm getting confused on terms like iSCSI storage virtualization and auto-Provisioning of massive (2TB) logical volumes -- can you help? I was searching the web for iSCSI target software and I wound up purchasing SANmelody software from DataCore. I thought I was getting disk virtualization, but then I tried something they call auto-provisioning of massive virtual volumes. Which is what I think of when I hear the term "storage virtualization". So what is the real definition?

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Welcome to the storage world of alphabet soup and technology confusion so let’s try to clarify things a bit. First iSCSI is a storage interface protocol that implements the SCSI command set over IP networks for performing block data access. Storage virtualization is a term that can mean well virtually anything and some vendors have gone to great lengths to stretch the meaning of storage virtualization. In general however storage virtualization and storage services describe functions including storage abstraction including volume management and Logical Units Numbers (LUNs) on storage volumes. It also can embrace storage aggregation also known as pooling of storage and LUNs implemented at the server, in a storage system, or in a fabric network. Storage virtualization can also include other functions such as remote mirroring and replication, data movement and migration, and other storage management functions. Some storage systems can dynamically expand storage volumes using available capacity however the servers operating system also needs to be able to support this feature. Software like DataCore SANmelody and others including some storage routers can provide iSCSI target support for attachment of Fibre Channel and other storage systems for pooling (aggregation) as well as volume management. A new technique being deployed by some vendors is the ability to let the server think that it has all of the storage required for a volume actually physically allocated when in reality only the amount of storage being used is allocated. This is referred to by some as thin provisioning or auto-provisioning. regarding 2TB volumes, that is actually a pretty common maximum volume size for a LUN on most storage subsystems and NAS filers today, after all, 5 x 400GB disk drives = 2TB. If you want to learn more about iSCSI, storage access and interface protocols, storage virtualizaiton, and management check out some of the free white papers at along with my book “Resilient Storage Networks” (Elsevier) at .


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