Abstract: A storage system may manage a logical unit using a differencing mechanism that captures changes to a base version of the logical unit. The logical unit may be presented to an operating system as a single storage device, while the logical unit may actually be provided by several storage devices that operate in conjunction with each other. In some cases, a single base version of the logical unit may be used to simultaneously provide multiple logical units, each of the logical units having a separate and independent differencing portion. In one such embodiment, a common base extent may contain read only versions of file blocks while each logical unit may contain independent differencing extents that contain changes to the base extent.

Abstract: An enlightened storage target may operate as a conventional storage target device, and may have additional capabilities to manage an initiator-target relationship under a service level agreement or quality of service agreement. An initiator may negotiate a service level agreement with the enlightened target, then the target may manage storage within the target device to meet the service level agreement. The target may also include a monitoring system that may monitor actual performance and compare the performance against the service level agreement. When the service level agreement is not being met, the target may alert the initiator and, in some cases, take precautionary or other actions until the service level agreement is either changed or is met.

Abstract: A storage system with a duplicate network storage device may change to and from a synchronous to asynchronous write connection based on a service level agreement. Degradation of a network connection or device performance may cause synchronous writes to be changed to asynchronous network writes, and synchronous writes may be performed on a second device. During the asynchronous operation, a differencing set may be created on a local storage device and used to update the network storage device. When the network storage device becomes able to meet the service level agreement with synchronous writes, the system may include the network storage device for synchronous writes.

Abstract: A remotely managed storage system may configure logical units using a low level storage controller on each managed computer system plus a target driver for each shared storage device. The storage controller may present logical units to operating systems running on a computer system and may operate on a lower level than a host operating system or hypervisor. A target driver may allow remote devices to use the local storage devices for other logical units. A storage master may configure the various components across a group of computers to create logical units of storage that are backed by multiple storage devices.