If you work with databases, you know how important it is to have a backup and recovery strategy in case of data loss or corruption. But do you know the difference between a hot and cold backup, and when to use each one? In this article, you will learn the basics of these two types of backups, their advantages and disadvantages, and some common scenarios where they are applied.
A hot backup, also known as an online backup, is a backup that is performed while the database is still running and accessible to users. This means that the backup does not interrupt the normal operations of the database, and the data is consistent with the current state of the database. However, a hot backup also has some drawbacks, such as requiring more storage space, consuming more system resources, and potentially affecting the performance of the database. A hot backup also requires the database to be in archive log mode, which means that every change made to the database is recorded in a separate file called a redo log. This allows the backup to capture the changes that occur during the backup process, and also enables point-in-time recovery, which is the ability to restore the database to a specific moment in time.
A cold backup, also known as an offline backup, is a backup that is performed while the database is shut down and not accessible to users. This means that the backup does not affect the normal operations of the database, and the data is consistent with the last state of the database before it was shut down. However, a cold backup also has some drawbacks, such as requiring downtime, which can be inconvenient or unacceptable for some applications, and not capturing the changes that occur after the backup is completed, which can result in data loss or inconsistency. A cold backup does not require the database to be in archive log mode, which means that it does not generate redo logs, and therefore does not enable point-in-time recovery.
A hot backup is suitable for scenarios where the database needs to be available 24/7, or where the downtime is minimal or scheduled. For example, a hot backup can be used for an e-commerce website, a social media platform, or a financial system, where the data is constantly changing and the users expect continuous service. A hot backup can also be used for incremental or differential backups, which are backups that only capture the changes since the last full or partial backup, respectively. This can reduce the backup time and size, and also provide more granular recovery options.
When there is a need for continuous system availability, hot backups are preferred. It's important to note that while hot backups offer the advantage of minimal downtime, they also come with challenges such as potential data inconsistencies and the need for sophisticated backup tools. Hot backup is used for 24/7 operations, real-time data requirements, critical business processes, dynamically changing environments, complex backup requirements for business and continuous SLA.
A cold backup is suitable for scenarios where the database does not need to be available all the time, or where the downtime is acceptable or planned. For example, a cold backup can be used for a test or development database, a historical or archival database, or a database that is only used during certain hours or days. A cold backup can also be used for full backups, which are backups that capture the entire database, regardless of the changes since the last backup. This can simplify the backup and recovery process, and also provide a consistent snapshot of the data.
Both cold backup and hot backup have specific features that make them uniquely tailored to meet the needs and demands of users. Similarly, cold backup functions only while the database is in shutdown and inaccessible to users as a strategy to guarantee the integrity of data which could be compromised if the backup occurs when data and files are in flux. On the other hand, hot backup is designed to run concurrently with the database actively online and accessible to users as a strategy to achieve faster work processes in multiuser systems. More fundamentally, the backup speed for hot backup is slow in comparison to cold backup’s fast backup speed.
There is no definitive answer to which type of backup is better, as it depends on various factors, such as the nature and size of the database, the frequency and schedule of the backups, the storage and performance requirements, the recovery objectives, and the business and operational needs. Therefore, it is important to evaluate the pros and cons of each type of backup, and also consider other factors, such as the backup software, the backup media, the backup location, the backup encryption, the backup verification, and the backup retention. Ultimately, the goal is to find a balance between the backup and recovery efficiency, reliability, and cost.