Abstract: Various embodiments of a computer system and methods are disclosed. In one embodiment, a computer system includes hosts coupled to a backup medium. The backup medium stores data segments and objects, each object referencing one or more segments. A second host conveys a write request to a first host identifying a data entity comprising segments referenced by a first object. The first host restores a copy of the data entity and creates a second object referencing the segments that were referenced by the first object in response to receiving the write request. The first host adds segment references to the second object in response to receiving a change that adds data to the copy or deletes a portion of a segment from the copy. The first host removes a segment reference from the second object if a change deletes all of a segment from the copy.

Abstract: Various embodiments of a computer system and methods are disclosed. In one embodiment, a computer system includes hosts coupled to a backup medium. The backup medium stores data segments and objects, each object referencing one or more segments. A second host conveys a write request to a first host identifying a data entity comprising segments referenced by a first object. The first host restores a copy of the data entity and creates a second object referencing the segments that were referenced by the first object in response to receiving the write request. The first host adds segment references to the second object in response to receiving a change that adds data to the copy or deletes a portion of a segment from the copy. The first host removes a segment reference from the second object if a change deletes all of a segment from the copy.

Abstract: A transparent yttrium oxide ceramic is made by densifying a yttrium oxide powder without addition of dopants. The yttrium oxide powder is consolidated into a body of a predetermined shape and sintered to a density such that any remaining porosity is sealed from the surrounding atmosphere. The closed porosity body is then subjected to an elevated pressure and temperature to provide the body with substantially 100% of theoretical density. The resulting body has substantial transparency over the wavelength range of 0.6 .mu.m to 7 .mu.m.