Image analysis – Image transformation or preprocessing – Image storage or retrieval
Reexamination Certificate
2001-05-11
2004-08-03
Do, Anh Hong (Department: 2624)
Image analysis
Image transformation or preprocessing
Image storage or retrieval
C711S114000, C714S006130
Reexamination Certificate
active
06771843
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus and methods for data storage in a computerized network or system. More particularly, the present invention relates to management of data at points in time using snapshot volumes of an original base volume, such that later-formed snapshot volumes are retained, rather than deleted, upon returning the base volume to the state of an earlier-formed snapshot volume.
BACKGROUND OF THE INVENTION
In a computerized data storage system, it is common to store data in a logical volume that changes over time as users access the data to add, delete and modify the data. For large databases or enterprise-critical data storage applications, it is often advantageous to preserve the state of the data at occasional or periodic time intervals using snapshot techniques or mirroring techniques. Such a preserved state is commonly used to return the data to a known stable state if the data ever becomes corrupted or invalid. In such a situation, the users experience only a short interruption in availability of the data before the data is once again accessible, albeit in an earlier state.
In snapshot techniques, as illustrated by
FIG. 1
, the data is contained in a primary, or “base,” logical volume
100
and various “snapshot” logical volumes
102
,
104
,
106
and
108
are formed therefrom at various times to preserve the state of the base volume
100
at those times. Each snapshot volume
102
-
108
contains data copied from the base volume
100
that was present in the base volume
100
at the time that the snapshot volume
102
-
108
was formed. When the base volume
100
is to be returned to the state of one of the snapshot volumes
102
-
108
, the data in the snapshot volume
102
-
108
is written back into the base volume
100
in a “rollback” procedure.
In snapshot techniques, it is typically assumed that if the data in the base volume
100
becomes invalid, then it is only the data that was added to or changed in the base volume
100
since the formation of the snapshot volume
102
-
108
that is incorrect. Therefore, the snapshot volume
102
-
108
contains only the original data that was present in the base volume
100
at the time the snapshot volume
102
-
108
was formed, but which has since been deleted from the base volume
100
or changed or replaced by new data within the base volume
100
. Thus, a rollback procedure returns the original data to the base volume
100
and removes any new data. Data that has not been changed in the base volume
100
since the formation of the snapshot volume
102
-
108
, on the other hand, is contained only in the base volume
100
and remains unaffected by a rollback.
After the snapshot volume (e.g.
104
) is rolled back into the base volume
100
, the snapshot volume
104
is no longer needed, so it may be deleted, unless it is desired to continue to preserve the state of the base volume
100
at the time the snapshot volume
104
was formed. An earlier-formed snapshot volume (e.g.
102
), since it preserves an earlier state of the base volume
100
, is typically maintained after the rollback of the snapshot volume
104
. Later-formed snapshot volumes (e.g.
106
and
108
), however, are invalidated and deleted, since the later states of the base volume
100
(at which the later-formed snapshot volumes
106
and
108
were formed) become superfluous after rolling back the base volume
100
to an earlier state. Thus, the later states are lost.
Mirroring techniques enable the preservation of states of a base volume
110
, as shown in
FIG. 2
, at various points in time by copying the entire base volume
110
into mirrored volumes
112
,
114
,
116
and
118
at those points in time. Since each mirrored volume
112
-
118
contains a complete copy of the base volume
110
at the points in time when the mirrored volumes
112
-
118
were formed, each mirrored volume
112
-
118
is effectively an independent logical volume. Therefore, upon rolling back one of the mirrored volumes (e.g.
114
) to the base volume
110
, it is possible to retain all of the other mirrored volumes
112
,
116
and
118
, including the later-formed mirrored volumes
116
and
118
, independently of the base volume
110
. However, the mirroring techniques, unlike the snapshot techniques, require considerable storage space to contain the mirrored volumes
112
-
118
and consume considerable processing time to form the mirrored volumes
112
-
118
.
It is with respect to these and other background considerations that the present invention has evolved.
SUMMARY OF THE INVENTION
The present invention utilizes snapshot techniques to preserve the state of a base volume at various points in time, but enables retention of later-formed snapshot volumes upon rolling back one of the snapshot volumes into the base volume. Thus, the present invention has the above described advantages of the snapshot and mirroring techniques for preserving states of the base volume without the disadvantages, such as losing later-formed snapshot volumes and consuming excessive processing time or storage space.
Upon rolling back one of the snapshot volumes to the base volume, the writes of the data from the rollback snapshot volume to the base volume are treated as ordinary writes to the base volume. Thus, data is copied from the base volume to any of the other snapshot volumes when necessary to preserve the states of the base volume at the points in time when the other snapshot volumes were formed. In this manner, the later-formed, as well as the earlier-formed, snapshot volumes can be retained after rolling back the base volume. It is possible, then, to “roll back” the base volume “forward” to the state of one of the later-formed snapshot volumes if desired.
A more complete appreciation of the present invention and its scope, and the manner in which it achieves the above noted improvements, can be obtained by reference to the following detailed description of presently preferred embodiments of the invention taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims.
REFERENCES:
patent: 5317731 (1994-05-01), Dias et al.
patent: 5487160 (1996-01-01), Bemis
patent: 5574851 (1996-11-01), Rathunde
patent: 5680580 (1997-10-01), Beardsley
patent: 6259828 (2001-07-01), Crinon et al.
patent: 6457098 (2002-09-01), DeKoning et al.
Prakash et al., “low-Cost Checkpointing and Failure Recovery in Mobile Computing system”, IEEE Transactions on Parallel an Distributed Systems, vol. 7, No. 10, Oct. 1996, pp., 1035-1048.
Huber Robin
Humlicek Donald R.
Do Anh Hong
LSI Logic Corporation
Maiorana P.C. Christopher P.
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