Patent Application
20240126777
The invention relates to the field of data storage, and in particular to techniques for creating clone volumes in multi-appliance clusters or federations of data storage systems.
A method is disclosed of creating a clone, on a second data storage appliance of a federation, of a source storage object stored on a first data storage appliance of the federation. The method includes, at the first data storage appliance, creating a snapshot (point-in-time copy) of the source storage object, and then performing a full copy of the snapshot from the first data storage appliance to the second data storage appliance to produce a copy snapshot on the second data storage appliance. At the second data storage appliance, the clone is created from the copy snapshot and incorporated into a federation-wide family association of the source storage object.
Several use cases are described, including (1) a clone on a different appliance from a base volume, (2) migrating a clone to a different appliance from a base volume, (3) refreshing a clone from a base volume, and a base volume from a clone, across appliances.
The technique can provide for flexibility and performance improvements based on applications separately using a primary volume on one appliance and a clone on another appliance.
The foregoing and other objects, features and advantages will be apparent from the following description of embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views.
Overview
A data storage system is disclosed as a scale out federation of highly available two node storage appliances that supports storage-oriented host attachment interfaces such as iSCSI, Fibre Channel and NVMe over Fabrics. The system supports block storage features, such as space-efficient volume clones and volume migration across appliances in a federation. In one embodiment, the data storage system may be incorporated into PowerStore™ data storage systems sold by Dell Technologies.
One limitation of existing data storage federations is an inability to create or migrate clones on a different appliance in a federation from the base volume. This limitation arises in part due to the way clones are realized, i.e., as derivative objects that share blocks with the primary object according to a block map. Multi-appliance federations generally do not support block sharing across appliances.
However, there are several potential use cases for the ability to locate clones on different appliances than their respective primary volumes. For example, such placement can be beneficial to run separate I/O intensive workloads on the base volume (e.g., a database application) and the clone (e.g., analytics application), such that I/O to the base volume runs through front-end ports on one appliance and I/O to the clone runs through front-end ports on a different appliance. Such a technique essentially provides a front-end I/O capacity scale out, enhancing system flexibility and performance.
Thus, disclosed herein is a technique for creating a clone on one appliance of a multi-appliance federation from a primary storage object located on another appliance of the federation. The technique can support various use cases including the following:
In operation, each DSS provides physical storage as well as various logical operations to provide data storage services to the clients 14, as generally known in the art. In particular, the DSSs 12 may provide storage structured as “volumes” having visibility to the clients 14. A volume may be viewed as a logical or virtual representation of a large unit of data storage, analogous to a physical “disk” or “device.” Modern data storage systems may host thousands of volumes using extensive underlying physical storage resources such as Flash memory arrays, magnetic media, etc. The clients 14 direct I/O requests to the volumes, and the DSSs 12 are responsible for translating the volume representation to a representation at the physical storage layer of operation, where volume data is physically stored.
The object layer 30 is responsible for maintaining the representations of volumes and other logical storage objects based on physical storage resources provided by the physical storage devices 26, as generally known in the art. This processing includes mapping logic that maps blocks of a logical representation to physical block addresses. It also includes maintaining representations and mappings for derivative storage objects such as clones and snapshots. As used herein, “clone” refers to a derivative object that can be the target of user I/O, for example in testing or other use separate from the use of a primary volume by an application. A snapshot is a point-in-time copy and is typically used in a read-only manner, e.g., for backup and recovery, or as here, as a mechanism for creating other derivative objects such as clones.
Derivative-storage functionality employs physical block sharing for efficient use of physical storage and other system resources. For example, a clone can be represented as a set of pointers to the same single set of physical storage blocks of a primary storage object. Similarly, a snapshot can be created as a set of pointers to a set of physical storage blocks that constitute a primary storage object at a given point in time. As the primary object later evolves, its block mappings and underlying physical storage generally diverges from those of the snapshot, and specialized functionality of the object layer 30 manages the block sharing to correctly represent both objects as operation proceeds.
Referring to
At 42, a full copy is performed of the snapshot from the first data storage appliance to a second data storage appliance (e.g., 12-2) to produce a copy snapshot on the second data storage appliance. “Full copy” refers to the need to copy all the data of the object, which is needed in part because of the inability to share blocks between appliances.
At 44, at the second data storage appliance, a clone is created from the copy snapshot and incorporated into a federation-wide family association of the source storage object. This on-appliance operation can employ block sharing for efficiency. As described more below, the clone can be maintained in synchronism with the storage object on the first appliance by subsequent update (refresh) operations. Going forward, the new clone can be the subject of user I/O to satisfy system operational needs, e.g., the above-mentioned scenario of having separate applications access the clone and the storage object from which it was created. The family representation is something visible to and maintained by the storage administrator 18, for purposes of managing the storage system and its constituent object as part of a larger data processing system.
As generally known, a volume family may have a tree-oriented structure, with higher nodes representing more foundational or primary objects and lower nodes representing successively derived objects. In the simple example of
It will typically be preferred that the above operation be performed during ongoing regular operation of the system, in which case it must be done as non-disruptively as possible. Detail on non-disruptive I/O cutover that can be utilized for clone migration is described in US Patent 10,789,018 “Supporting non-disruptive movement of a logical volume of non-volatile data storage between storage appliances” to Tylik, et al.
The above approach can be expanded to migration of a clone that is an intermediate node in a clone tree and not a leaf. For such a clone, after the above steps are performed and the new clone 60-M is added into the base volume family, the next step is to copy the relationships with the original “parent’ and “child” clones and snapshots. The process can be applied recursively to effect migration of a clone subtree including both node and leaf clones.
While various embodiments of the invention have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.
