Some solutions marketed as continuous data protection may only allow restores at fixed intervals such as 1 hour, or 24 hours. Such schemes are not universally recognized as true continuous data protection, as they do not provide the ability to restore to any point in time. Such solutions are often based on periodic snapshots, an example of which is CDP Server, disk-based backup software that periodically creates restore points using a snapshot and volume filter device driver to track disk changes. There is debate in the industry as to whether the granularity of backup must be “every write” to be CDPm, or whether a solution that captures the data every few seconds is good enough. The latter is sometimes called near continuous backup. The debate hinges on the use of the term continuous: whether only the backup process must be continuous, which is sufficient to achieve the benefits cited above, or whether the ability to restore from the backup also must be continuous. The Storage Networking Industry Association (SNIA) uses the “every write” definition.
Continuous data protection differs from RAID, replication, or mirroring in that these technologies only protect one copy of the data (the most recent). If data becomes corrupted in a way that is not immediately detected, these technologies simply protect the corrupted data.
Continuous data protection protects against some effects of data corruption by allowing restoration of a previous, uncorrupted version of the data. Transactions that took place between the corrupting event and the restoration is lost, however. They could be recovered through other means, such as journaling.
In some situations, continuous data protection requires less space on backup media (usually disk) than traditional backup. Most continuous data protection solutions save byte or block-level differences rather than file-level differences. This means that if you change one byte of a 100 GB file, only the changed byte or block is backed up. Traditional incremental and differential backups make copies of entire files.
Continuous Data Protection
Continuous Data Protection (CDP) is a concept that is been in play for the past decade or longer. Vendors have differing ways to deliver CDP, or near-CDP as some have begun marketing it. Continuous data protection (CDP), also called continuous backup or real-time backup, refers to backup of computer data by automatically saving a copy of every change made to that data, essentially capturing every version of the data that the user saves.
CDP runs as a service that captures changes to data to a separate storage location. There are multiple methods for capturing the continuous changes involving different technologies that serve different needs. CDP-based solutions can provide fine granularities of restorable objects ranging from crash-consistent images to logical objects such as files, mail boxes, messages, and database files and logs. So why should you be aware of CDP? I do backups already so what does CDP bring to the table that you should be concerned with?
It’s not about backing up or continuously backing up – it’s about restoring your data so your business can be back up and running as quickly as possible with the least amount of data loss.
Traditional backup is scheduled at specific times of the day, week and month. The idea of keeping monthlies for a certain period of time; weeklies for another period of time and dailies for a period of time so that companies could recover from a specific point in time.
True CDP is writing byte or block-level changes to your data rather than file-level differences. This process saves you disk space and allows for actual point-in-time recovery.
Continuous data protection is different from traditional backup in that you don’t have to specify the point in time to recover from until ready to restore. Traditional backups only restore data from the time the backup was made. Continuous data protection has no backup schedules. When data is written to disk, it is also asynchronously written to a second location, usually another computer over the network. This introduces some overhead to disk-write operations but eliminates the need for scheduled backups.