The common and widely used Backup Architecture is based on the Server-Client model. Any backup architecture is composed of the following four components.
- Backup Servers
- Backup Clients
- Media Servers
- Backup Destinations/Targets
The backup server manages the backup operations and maintains the backup database, which contains information about the backup configuration and backup metadata. The backup configuration contains information about when to run backups, which client data to be backed up, and so on. The backup metadata contains information about the backed up data.
The role of a backup client is to gather the data that is to be backed up and send it to the backup server. The backup client can be installed on application servers, mobile clients, and desktops. It also sends the tracking information to the backup server.
Media Servers connect to the backup destinations and make it available to backup clients so that they can send data to the backup target. In IBM TSM terminology, media servers are referred as Primary Library Manager and other TSM servers as Library Clients. The media servers controls one or more backup devices. Backup devices may be attached directly or through a network to the Media Servers. The Media Servers sends the tracking information about the data written to the backup device to the backup server. Typically this information is used for recoveries. For example, a media server might be connected to a pool of storage over an FC network and make that storage available to backup clients over an SAN.
A wide range of backup destinations/targets are currently available such as tape, disk, and virtual tape library. Traditional backup solutions primarily used tape as a backup destination and modern backup approaches tend to use disk based pools which are shared over SAN or LAN. Disk arrays can also be used as virtual tape libraries to combine the benefits of Disk and Tape. Now, organizations can also back up their data to the cloud storage. Many service providers offer backup as a service that enables an organization to reduce its backup management overhead.
The backup window is another term that relates to backup and business continuity. A backup window is a period of time during which data can be backed up. For example, most organizations consider the time between 6 PM to 6 AM as the ideal backup window as there will be less activity on the servers. However, many businesses have different backup windows for different applications, depending on core business hours for those applications. A major reason for the backup window is that backups often negatively impact the performance of the system being backed up, so backing up a critical system during the core business day is usually not a good idea.
Different Types of Backup Destinations/Targets
Tape Library and Tape Drives
A tape library contains one or more tape drives that records and retrieves data on a magnetic tape. Tape is portable, and one of the primary reasons for the use of tape is long-term, off-site storage. Backups implemented using tape devices involve several hidden costs. Tapes must be stored in locations with a controlled environment to ensure preservation of the media and to prevent data corruption. The advantage of using tape drives as backup target is that modern tape drives and tape libraries have high capacity, high sequential performance and low power. The common disadvantages of tapes are they are subject to degradation over time, especially if they aren’t stored in optimal conditions. Even though you have stored the tapes in optimal conditions, it is possible that you no longer have any tape drives or software that can read them. In addition, tapes are great at restoring data from full backups, but if you have to perform restores based on differential backups, they can take huge time.
Physical transportation of the tapes to offsite locations also adds management overhead and increases the possibility of loss of tapes during offsite shipment. Due to its sequential data access, both backing up of data and restoring it take more time with tape, and this may impact the backup window and RTO. Data integrity and recoverability are also major issues with tape-based backup media. Because of these concerns, as well as the drop in the cost of spinning disk media, many people are starting to move away from tape for backups.
Another backup target which is widely used in backup infrastructure is the Disk Drives. The commonly used disk drives are Hard Disk Drives (HDD) and Solid State Drives (SSD). Hard Disk Drives gives better performance than Solid State Drives. Disk density has increased dramatically over the past few years, lowering the cost per gigabyte to the point where it became a viable backup target for organizations. When used in a highly available configuration in a storage array, disks offer a reliable and fast backup target medium. One way to implement a backup-to-disk system is by using it as a staging area, offloading backup data to a secondary backup target such as tape after a period of time (generally referred as migration). Some vendors offer a purpose-built, disk-based backup appliances that are emerged as the optimal backup target solution. These systems are optimized for backup and recovery operations, offering extensive integration with popular backup management applications. The built-in features such as replication, compression, encryption, and data deduplication increase the value of purpose-built backup appliances.
Virtual Tape Libraries
Virtual tape libraries use disks as backup media. Virtual tapes are disk drives that are emulated and presented as tapes to the backup software. Compared to physical tapes, virtual tapes offer better performance, better reliability, and random disk access. A virtual tape drive does not require the usual maintenance tasks associated with a physical tape drive, such as periodic cleaning and drive calibration. Compared to the disk library, a virtual tape library offers easy installation and administration because it is preconfigured by the manufacturer. A key feature that is usually available on virtual tape library appliances is replication.
Taking backup to the Cloud
Since everything is going to cloud now, we can use cloud to send the backups as well. A common approach is to deploy a disk-to-disk-to-cloud (D2D2C) architecture. This is similar to disk-to-disk-to-tape (D2D2T), with the tape being replaced by the cloud. In this architecture, the disk-to-disk portion still occurs within your data center, utilizes deduplication technology, and transfers only deduplicated data to the cloud for long-term retention, where it’s not expected to be required for restore operations as often as the data that is on premise on the intermediary disk backup platform. Deduplication technology and synthetic full backups, or other incremental forever approaches, also help here. It should also be noted in this D2D2C architecture that only a portion of the backup estate exists in the cloud.
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