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In OneFS 8.2 and later, SnapshotIQ adopts a domains model for governance of scheduled snapshots. By using the OneFS IFS domains infrastructure, recurring snapshot efficiency and performance is increased by limiting the scope of governance to a smaller, well defined domain boundary.
IFS Domains provide a Mark Job that proactively marks all the files in the domain. Creating a snapshot on a fully marked domain will not cause further “painting” operations, thereby avoiding a significant portion of the resource overhead caused by taking a new snapshot.
Once a domain has been fully marked, subsequent snapshot creation operations will not cause any further painting. The new snapshot ID is simply added to the domain data section, so the creation of a new snapshot will not trigger a system-wide painting event anymore. Domains are reused whenever possible.
Creating two domains of the same type on the same directory will cause the second domain to become an alias of the first domain. Aliases do not require marking since they share the existing marks. This benefits both snapshots and snapshot schedules taken on the same directory. For all these reasons, the number of I/O and locking operations needed to resolve snapshot governance is greatly reduced. Because the SnapIDs are stored in a single location (as opposed to being stored on individual inodes), this greatly simplifies Snapshot ID garbage collection whenever a Snapshot is deleted. By leveraging IFS Domains, creating a snapshot on a domain that is fully marked will not cause further “painting” operations, so a significant portion of the performance impact caused by taking a new snapshot is avoided.
The figure above shows an example of domain-based snapshots. In this case, a snapshot was taken on the ‘projects’ directory, and on the directory named ‘video’. File v1.mp4 is tagged with the domain IDs, making it more efficient to determine snapshot governance.
A snapshot of file v1.mp4 creates a snap_ID in the domain’s SBT (system b-tree) providing a single place to store snapshot metadata. In previous OneFS versions, snapIDs were stored in the inode, which resulted in duplication of the snap_IDs and metadata usage.
Only snapshots taken after an upgrade to OneFS 8.2 or later will use IFS domains backing. Any snapshots created prior to the upgrade will not be converted and will remain in their original form.
Also, IFS Domains brings other benefits including: