What Is Snapshot?
A storage snapshot is a set of reference markers for data at a specific point in time.
How Does Snapshot Work?
Storage snapshots are usually based on the use of differencing disk.
All future writes are directed to the differencing disk, leaving the original virtual hard disk unchanged.
The filesystem is completely unaware of the existence of diff disks.
The file system continues to behave as if it were on a physical machine.
Snapshots have a parent-child relationship and form a tree.
Each snapshot taken creates another branch of the tree.
Storage snapshots can be used for disaster recovery (DR) when information is lost due to human error.
Snapshots can also be used to restore the system to a previous state if the wrong patch is installed.
throw in of Snapshot
The implementation of storage snapshot technology varies by vendor.
There are different types.
Disadvantages:However, they are performance intensive as each snapshot requires one read and two writes.
Redirect-on-Write Snapshot
Redirect-on-write snapshots use pointers to reference snapshot-protected blocks.
Disadvantage:redirect-on-write snapshots rely on the original block.
Other modifications create new blocks.
If the snapshot is deleted, the coordination between multiple new blocks and the original block becomes complicated.
Advantages:Easier data recovery, replication and archiving.
Even if the primary/original copy is lost, the entire volume is still available.
Continuous Data Protection (CDP)
CDPcreates frequent snapshots of raw data triggered by setting policies.
Ideally, CDP snapshots are created in real-time.
This means that every time a change is made, the snapshot of the original copy is updated.
Advantages:Reduces recovery point objective(RPO) to almost zero.
Disadvantages:Frequent snapshot creation and updates consume performance and bandwidth (if over web connection storage).
Typically, snapshots are created using disk/system images or system restore and recovery software.
However, most backup software can also take snapshot backups and restore the system using snapshots.
What are the differences between snapshot and backup?
This article compares them in both VMware and SQL servers.
