In contrast, the purpose of a backup is to store data in the short and medium term, providing a regular snapshot of the data in question. This concept allows copies of whole data sets to be made so that they can be swapped out to external storage or a cloud environment and restored at a later date. How using 'Azure backup' to backup a VM is different from taking the snapshots of OS Disk and data disk of azure VM via 'az vm' cli commands? The biggest difference is that, we can use Azure Backup to restore VM directly. If we use snapshot and want to restore VM, we have to use snapshot to create OSdisk and then use this OSdisk to create new VM. I understand you would like to know the difference in the features of AWS Backup and the normal volume snapshots regarding the data inconsistency. Today, several AWS services offer backup features that help you protect your data, such as EBS snapshots, RDS snapshots, DynamoDB backups, and Storage Gateway snapshots.
What does a snapshot do?
In the event of data loss or a ransomware attack, restoration of the data, site structure, and permissions can be a long, and sometimes manual process — unless your data has been backed up. Backup: Data Recovery. When it comes to recovering data, there are marked differences between sync and share services and backup recovery. Delta backups only capture the data changed since the last backup or delta backup, meaning less log backups are read for a recovery. There are two options available when creating a delta backup: Differential Backup – stores all data changed since the last full backup.
In short snapshots are versioning, or the ability to undo a change. If you take a snapshot every hour, for example, then all your files or folders can be reverted back to the state they were at the time of any of your snapshots. So, if you get a virus, then you can just revert your files, folders, or whole volume to the state it was before you got the virus
How is this different than a backup?
A backup is a complete copy of your data. So, if you have 5TB of data each copy will take up an additional 5TB of space. If you make a backup every 1 hour, then after just 10 hours, your backups would take 50TB of space. For this reason, it is not common to save many versions of your backups and backups are not good for versioning.
Snapshots are great for versioning because they are not backups and they can have many versions without taking up much space. A snapshot only needs to save enough information to undo a change and that makes it take less space than a backup.
How do QNAP’s block-level snapshots work?
When you take a snapshot, the metadata recording where each block of data is stored is copied to the snapshot. This takes very little space and the snapshot is created very quickly. From then on, any time you change a block of data, that block is written to a designated snapshot space. The current metadata is updated to reflect the change as well. This procedure is called “Redirect on write”.
Because your snapshot has the metadata, it can recognize what blocks of data have been added or changed since the creation of the snapshot. If you revert to one of your snapshots, every block of data that was added or changed since the snapshot was taken is removed from where it is saved in the snapshot. Then every block of data is as it was at the time the snapshot was taken. And since your files are made up of blocks of data, every file is now as it was when the snapshot was taken.
This allows you to undo changes to your files, folders, and even volume, or to bring back files you have deleted accidentally.
What is good about the way QNAP does snapshots?
Easy to navigate interface:
Just click on what snapshot you want to load, and then you can revert the whole volume or select a specific file or folder to restore.
You can also easily schedule snapshots or take one manually at any time on the same interface.
Block-level:
Because QNAP does block level snapshots, they are more space efficient than file level snapshots. With file level snapshots, if you make even a small change to a file, you need to save the whole file to the snapshot. But with block level snapshots, you only need to save the blocks within the file that have been changed.
Much better for iSCSI LUNs:
Block level snapshots let you take snapshots of any volumes or LUNs on your NAS including a block level iSCSI LUN. Other snapshots that rely on BTRFS cannot do this because they can only take a snapshot of a volume & a thin LUN managed by the BTRFS file system.
Control snapshot space allocation to keep your NAS functional:
QNAP built their snapshots from the ground up and gave you more control of how space for the snapshots is allocated. You control how much storage to reserve for the snapshots. And other files and applications will have priority over the space that you did not allocate to snapshots.
For other NAS providers that rely on BTRFS, you have less control, and sometimes the snapshots can take up so much space that the NAS is no longer functional as a file server.
When are snapshots small?
When you only add files to the NAS, you don’t need to save blocks of data to the snapshot. The Snapshot just needs to have the metadata recording what blocks have been added to the NAS since the creation of the snapshot.
What makes a snapshot big?
When you delete files, the snapshot needs to be able to restore the files you deleted. To do that, any block of data you delete and overwrite will be saved to the snapshot. Saving blocks of data to the snapshot takes much more space than just saving metadata. So, deleting files makes your snapshot size grow much more than adding file
Conclusion:
Most people delete some files and make some changes to their files, but not enough to make the snapshots get too big. The default for QNAP is to allocate 20% of your storage space for snapshots and this is usually more than enough to have 256 snapshots. You could never get close to this many complete backups without taking up huge amounts of space. That is why snapshots are much better than backups for versioning. But snapshots don’t protect you from drive failure so it is still good to have RAID redundancy and at least one backup of your data to another device.
(Originally posted on April 24, 2018; contents updated by Michael Wang)
Data backup and data archive are two terms which are often mentioned in the same breath and on the surface may seem to be almost analogous. After all, they both involve making a copy of a business’s data for future use. However, that is where the similarities end.
A backup and an archive are actually used for completely different purposes and are quite different in a number of ways. Below, we have highlighted some of the key differences between a backup and an archive and the critical common features which are important in both.
Purpose
A backup is a copy of your current and active data which can be used for operational recoveries in the event that your data is lost or corrupted in some way. The main purpose of a backup is to restore your data to a previous point in time. Archives, on the other hand are intended to be used as repositories for data which needs to be kept for a long period of time but is not necessarily important for operational activities. For example, data which must be retained for regulatory compliance only may be archived but would not necessarily be suitable for backup.
Data Backup vs. Archive
The data stored in a backup is a copy of the current and active operational data in use by a business. This includes files which are currently being accessed and changed on a regular basis. The files stored on an archive are generally no longer in use, not changing frequently and not required on a regular basis. As such, employees will not be affected if these files are moved from a business’s regular storage. However, through file stubbing, files stored in an archive can still be made easily accessible to employees.
Location
A backup is simply a copy of the current and active information stored on your servers. When a backup copy of your data is created, the original files are not affected and still reside in the same location. While an archive is also a copy of your data, the archiving process relocates the data from your business’s primary storage location and moving it on to less expensive and more long-term storage locations.
Speed
As the purpose of a backup and an archive are different, the features valued in each are also different. With a backup, speed is an important attribute. As backups are often made regularly to keep them current, it is essential that they can be completed quickly. Equally as important is the ability to quickly recover and restore data in the event of data loss as a quick backup procedure allows your business to limit the operational impact.
Searchability
Difference Between Backup And Snapshot
The ability to easily search for and locate a file is of vital importance with a data archive. An archive can potentially contain a huge amount of data built up over several years and it is unlikely that the location of specific files and folders will be known. It is incredibly important that these files can be found in a quick and efficient manner not only for compliance reasons but also in the event that a legal request is made.
Duration
Data Backup Services
The length of time the data stored in a backup is much shorter than an archive. Depending on its operational importance, the data stored in a backup may be updated as frequently as daily or even multiple times a day. As such, the data is only required for a short period of time. Archives on the other hand may store large amounts of data for many years. For this reason, the integrity of retained data over longer time periods is of great importance.