Three types:
Full--back up everything and reset archive bit.
Incremental--backup everything since last full or incremental and reset archive bit. Backup about the same amount of data each day. This method takes a short amount of time to take the backup, but would be the longest to restore. To restore, restore the full then restore each incremental backup.
Differential or cumulative--back up everything since last full backup. The backup and time to take the backup continues to grow as time elapses from the last full backup. As time elapses, this one requires to most time to take the backup. It would be the quickest restore since you would restore the full then the last differential backup.
Terms:
RTO: Recovery Time Objective--how long to restore.
RPO: Recovery Point Objective--to what point in time should the restore go to.
Data Deduplication:
There are two methods of deduplication: file level and subfile level. Determining the uniqueness by implementing either method offers benefits; however, results can vary. The differences exist in the amount of data reduction each method produces and the time each approach takes to determine the unique content.
File-level deduplication (also called single-instance storage) detects and removes redundant copies of identical files.
Subfile deduplication breaks the file into smaller chunks and then uses a specialized algorithm to detect redundant data within and across the file. As a result, subfile deduplication eliminates duplicate data across files. There are two forms of subfile deduplication:
fixed-length block and variable-length segment. The fixed-length block deduplication divides the files into fixed length blocks and uses a hash algorithm to find the duplicate data. Although simple in design, fixed-length blocks might miss many opportunities to discover redundant data because the block boundary of similar data might be different. Consider the addition of a person's name to a document's title page. This shifts the whole document, and all the blocks appear to have changed, causing the failure of the deduplication method to detect equivalencies.
In variable-length segment deduplication, if there is a change in the segment, the boundary for only that segment is adjusted, leaving the remaining segments unchanged. This method vastly improves the ability to find duplicate data segments compared to fixed-block.
Source-based data deduplication eliminates redundant data at the source before it transmits to the backup device. Source-based data deduplication can dramatically reduce the amount of backup data sent over the network during backup processes. It provides the benefits of a shorter backup window and requires less network bandwidth. There is also a substantial reduction in the capacity required to store the backup images.
Target-based data deduplication is an alternative to source-based data deduplication. Target-based data deduplication occurs at the backup device, which offloads the backup client from the deduplication process.
Inline deduplication performs deduplication on the backup data before it is stored on the backup device. Hence, this method reduces the storage capacity needed for the backup. Inline deduplication introduces overhead in the form of the time required to identify and remove duplication in the data. So, this method is best suited for an environment with a large backup window.
Post-process deduplication enables the backup data to be stored or written on the backup device first and then deduplicated later. This method is suitable for situations with tighter backup windows. However, post-process deduplication requires more storage capacity to store the backup images before they are deduplicated.
Archives:
An archive can be implemented as an online, nearline, or offline solution:
- Online archive: A storage device directly connected to a host that makes the data immediately accessible.
- Nearline archive: A storage device connected to a host, but the device where the data is stored must be mounted or loaded to access the data.
- Offline archive: A storage device that is not ready to use. Manual intervention is required to connect, mount, or load the storage device before data can be accessed
There are two methods of deduplication: file level and subfile level. Determining the uniqueness by implementing either method offers benefits; however, results can vary. The differences exist in the amount of data reduction each method produces and the time each approach takes to determine the unique content.
File-level deduplication (also called single-instance storage) detects and removes redundant copies of identical files. It enables storing only one copy of the file; the subsequent copies are replaced with a pointer that points to the original file. File-level deduplication is simple and fast but does not address the problem of duplicate content inside the files. For example, two 10-MB PowerPoint presentations with a difference in just the title page are not considered as duplicate files, and each file will be stored separately.
Subfile deduplication breaks the file into smaller chunks and then uses a specialized algorithm to detect redundant data within and across the file. As a result, subfile deduplication eliminates duplicate data across files. There are two forms of subfilededuplication: fixed-length block and variable-length segment. The fixed-length block deduplication divides the files into fixed length blocks and uses a hash algorithm to find the duplicate data. Although simple in design, fixed-length blocks might miss many opportunities to discover redundant data because the block boundary of similar data might be different. Consider the addition of a person's name to a document's title page. This shifts the whole document, and all the blocks appear to have changed, causing the failure of the deduplication method to detect equivalencies. In variable-length segment deduplication, if there is a change in the segment, the boundary for only that segment is adjusted, leaving the remaining segments unchanged. This method vastly improves the ability to find duplicate data segments compared to fixed-block.
In a serverless backup, the network share is mounted directly on the storage node. This avoids overloading the network during the backup process and eliminates the need to use resources on the application server. Figure 10.12 illustrates serverless backup in the NAS environment. In this scenario, the storage node, which is also a backup client, reads the data from the NAS head and writes it to the backup device without involving the application server. Compared to the previous solution, this eliminates one network hop.
In the NDMP 3-way method, a separate private backup network must be established between all NAS heads and the NAS head connected to the backup device. Metadata and NDMP control data are still transferred across the public network. Figure 10.14shows a NDMP 3-way backup.
Image-based backup operates at the hypervisor level and essentially takes a snapshot of the VM. It creates a copy of the guest OS and all the data associated with it (snapshot of VM disk files), including the VM state and application configurations. The backup is saved as a single file called an “image,” and this image is mounted on the separate physical machine–proxy server, which acts as a backup client. The backup software then backs up these image files normally. (see Figure 10.22). This effectively offloads the backup processing from the hypervisor and transfers the load on the proxy server, thereby reducing the impact to VMs running on the hypervisor. Image-based backup enables quick restoration of a VM.
NDMP is an industry-standard TCP/IP-based protocol specifically designed for a backup in a NAS environment. It communicates with several elements in the backup environment (NAS head, backup devices, backup server, and so on) for data transfer and enables vendors to use a common protocol for the backup architecture. Data can be backed up using NDMP regardless of the operating system or platform. Due to its flexibility, it is no longer necessary to transport data through the application server, which reduces the load on the application server and improves the backup speed.
NDMP optimizes backup and restore by leveraging the high-speed connection between the backup devices and the NAS head. In NDMP, backup data is sent directly from the NAS head to the backup device, whereas metadata is sent to the backup server.Figure 10.13 illustrates a backup in the NAS environment using NDMP 2-way. In this model, network traffic is minimized by isolating data movement from the NAS head to the locally attached backup device. Only metadata is transported on the network. The backup device is dedicated to the NAS device, and hence, this method does not support centralized management of all backup devices.
In the NDMP 3-way method, a separate private backup network must be established between all NAS heads and the NAS head connected to the backup device. Metadata and NDMP control data are still transferred across the public network. Figure 10.14shows a NDMP 3-way backup.
Image-based backup operates at the hypervisor level and essentially takes a snapshot of the VM. It creates a copy of the guest OS and all the data associated with it (snapshot of VM disk files), including the VM state and application configurations. The backup is saved as a single file called an “image,” and this image is mounted on the separate physical machine–proxy server, which acts as a backup client. The backup software then backs up these image files normally. (see Figure 10.22). This effectively offloads the backup processing from the hypervisor and transfers the load on the proxy server, thereby reducing the impact to VMs running on the hypervisor. Image-based backup enables quick restoration of a VM.
