Snapshot

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About Snapshot

Snapshot is a feature used to create a logical usable image and/or an independent fully usable copy of the data residing on a virtual disk at a specific point in time (snapshot point). At the moment a snapshot is created from a virtual disk, the data contained on the "source" virtual disk is logically or physically copied to another virtual disk, referred to as the "snapshot." Snapshots can be served to hosts.

The difference between the Continuous Data Protection (CDP) feature and the Snapshot feature is that the snapshot preserves the contents of the virtual disk at a point in time, while a CDP-enabled virtual disk allows the creation of a rollback at any point in time preserved in the history log. It is possible to create a snapshot at a time when the data is in a known good state and this is the best practice. In the case of a rollback, the image is created regardless of the state.

Benefits of Snapshot

Snapshots provide a foundation to solve the following types of problems:

Disaster Protection – Snapshots provide an efficient way to identify and return to specific virtual disk data.
Application Testing – Snapshots provide a way to perform test activities on a consistent and re-usable copy of operational data while the source data remains unaltered. Exposure to data corruption and system failure can be minimized by testing against a persistent image of real data before bringing new application changes online.
Fast Data Cloning – Snapshots provide a way to duplicate data quickly without disruption of data availability.
Error Protection – Snapshots provide a way to perform faster and more frequent backups translating to faster recovery from data corruption problems.
Alternative to File-level Data Sharing – Snapshots provide a way to present multiple copies of the same virtual disk to multiple hosts. In other words, multiple users can have individual copies of the same data. Use snapshots to provide file-level data sharing in order to:
- Off-load machine cycles related to sharing data between machines
- Reduce data traffic in the SAN/LAN
- Increase performance and data availability
- Allow better scalability

Snapshot Types

There are two snapshot types:

Differential Migration – The "snapshot" is an image of the "source" virtual disk at the time of the snapshot (snapshot point). The image is logical and dependent on the source.
Deleting the source virtual disk, also deletes any differential snapshots due to their dependency on the source. Differential snapshots are not protected against unexpected restarts of the DataCore Server.
Full Migration – The "snapshot" is a tangible clone copy of the "source" virtual disk at the time of the snapshot (snapshot point). After migration is successfully completed, the snapshot is fully usable and can exist and operate independently of the source from which it was created.

After creating snapshots, additional operations can be performed, see Performing Snapshot Operations. Snapshot operations can also be performed on virtual disk groups, see Virtual Disk Groups for more information.

Snapshot Mapstore

The mapstore is a dedicated storage location within a disk pool that is used internally for the specific purpose of holding state and delta map information for all snapshots on the source DataCore Server. The mapstore ensures that snapshots remain valid when a server is stopped or restarted. It does not protect against unexpected computer restarts.

The first time a snapshot is created on a server, the disk pool where the mapstore will reside can be selected. The mapstore can add up to 256 GB of virtual disk allocated space in the pool.

The mapstore is hidden, but the disk pool containing the mapstore can be displayed and changed in the DataCore Server Details page>Settings tab.

Delta Map

The delta map is a record of the differences between the source virtual disk and the snapshot. The delta map is displayed as a whole number percentage. The percentage will be displayed as 0% until 1% is reached. If you update the snapshot, the delta map will be reset to 0%.

The delta map percentage can be viewed in the Virtual Disk Details page>Snapshots tab for the source virtual disk or in the Snapshot Details page.

Migration Map

Migration Map is a record of the amount of data that has been migrated to the snapshot. The migration map is displayed as a whole number percentage. The percentage will be displayed as 0% until 1% is reached.

The migration map percentage can be viewed in the Snapshot Details page.

Preferred Snapshot Pool

A pool can be designated as the preferred pool to use when creating snapshots for a virtual disk. The preferred snapshot pool is set per virtual disk in the Virtual Disk Details page>Settings tab. When set, all snapshots for that virtual disk will be created from the designated pool. See Snapshot Operations for more information.