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Related concepts of snapshot technology


Snapshot technology is generally defined as a set of files or directories or copies of a volume at a specific point in time. What it can capture is an image of some specific data at a specific point in time. The emergence of snapshot technology is to solve some backup problems we often encounter, including, the amount of data to be backed up is too large to complete the backup in a limited period of time.

Moving files from a directory that has not been backed up to a directory that has been backed up often leads to backup failure. Since some files are being written at the time of backup, some backup data cannot be used.

Hot backup seriously affects the performance of the application system, etc.
All the above common backup problems can be solved by snapshot technology. However, we can not simply regard snapshot as a panacea to solve all problems, because snapshot technology needs to be further improved. (e.g. snapshot consistency issue)

To create a snapshot, different devices need different commands, but for the system, it basically includes the following steps:
1. First, it initiates the creation instruction;
2. At the start time point, the instruction informs the operating system to suspend the operation of application programs and file systems;
3. Refresh the file system cache and end-all read and write transactions;
4. Create snapshot points;
5. After the creation is completed, release the file system and application, and the system returns to normal operation.
Now, snapshot technology has gone beyond simple data protection. We can use snapshots for efficient and risk-free application testing. Testing with snapshot data will not cause any damage to production data. Snapshot is also an ideal test data source for data mining and eDiscovery applications. In terms of disaster recovery, a snapshot is a very effective method - even the first choice. It is very suitable for data recovery in the event of logical errors such as malicious software attack, human error operation, and data corruption.

We think that only disk array has snapshot function, but in fact, disk array is only one of them. Generally speaking, snapshot technology can have seven different types of implementation subjects:
1. Host file system (including server, desktop computer, and notebook computer);
2. Logical volume manager (LVM);
3. Network-attached storage system (NAS);
4. Disk array;
5. Storage virtualization device;
6. Host virtualization management program;
7. Database.
For the File system based snapshot, many file systems support the snapshot function. Microsoft's Windows NTFS has VSS volume shadow copy services (Vista called shadow copy); sun Solaris's latest file system ZFS (zettabyte file system); Apple's Mac OS X 10.6 (snow leopard); Novell storage services (NSS) of Novell Netware 4.11 (or higher); OES Linux under Novell SUSE Linux operating system, etc.

Meanwhile, Vinchin Backup & Recovery also supports the virtualized PIN platform mentioned above and also provides, serial Snapshot and parallel Snapshot, When you perform a backup job, Serial snapshot is a technology to take a snapshot of the target VMs in turn and transfer the backup data from the production area to the backup area in turn, while the parallel snapshot is to take a snapshot of the target VMs concurrently and transfer the backup data in turn. If you have large numbers of VMs to be backed up,  choosing “Parallel Snapshot" will occupy a lot of computing resources and storage space of the production area, so it is recommended to choose “Serial Snapshot” in this situation; Only if there’s the business relationship between the target VMs or when time consistency of all backup data is required, it is recommended to choose “Parallel Snapshot”. Either serial snapshot or parallel snapshot will cause the same backup time.

  • Tag:
  • Virtualization

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