Partial-Cumulative Incremental (level n)
A specialized form of Incremental Backup which backs up the files that have been modified or created since the most recent backup at the same level or lower (level n or lower).
One way to understand what a PCI Backup is and how it behaves is to compare it to the more traditional Cumulative Incremental (CI) Backup. The CI Backup is commonly used by vendors that support multiple backup levels. These multiple level backups are usually defined as level 0 through level 9. A level 0 backup is usually considered a “full” or “complete” backup. Many complex level backup strategies may be implemented. Multiple levels of backup allow site administrators to reduce the frequency of periodic full backups. For simplicity, we will consider a typical 3 level strategy consisting of monthly (level 0), weekly (level 1) and daily (level 2) backups.
The figure above shows how the sizes of two partial cumulative incremental backup levels, daily (level 2) and weekly (level 1), can change over time. The level 2 daily backup copies only changes since the last client backup, essentially flattening the size of each daily backup. The level 1 weekly backup (Days 7 and 14), works in the same way to only copy changes since the last level 1 weekly backup. As the name implies, as data changes over time, it is partially accumulated at various backup levels. A new full backup will signal the beginning of a new backup cycle, but is not required to reset the size of the higher level weekly and daily backups.
These graphs were generated using backup statistics gathered from a production backup server. The data has been graphed with respect to the size of the corresponding Differential Backup to show the increased savings that PCI Backups provide over CI Backups. In this two week sample, 2 level PCI Backups were 36% smaller than the corresponding CI Backups and 58% smaller than the corresponding Differential Backup.
The new PCI Backups will typically be significantly smaller in size at any backup level than currently available CI Backups. The primary reason for this is that each PCI Backup contains data changes over a smaller, fixed period of time. This “flattens” the size of the backup at each level and allows any number of backups to be taken at each level without ever increasing backup sizes. As the number of backups per each cycle increases, the savings that PCI Backups provides over CI Backups will continue to increase as well.
You may have noticed that the Partial Cumulative Incremental backup volume is actually smaller than the sum of the daily True incremental Backup volumes added together. This is because a True incremental Backup volume consists of both new and changed data. The Partial Cumulative Incremental is new or changed data since the most recent backup at the same level or lower. Therefore, the PCI volume will almost always be smaller than the sum of the TI volumes.
See Also: Teradactyl white paper on new advancements in synthetic backup consolidation of partial cumulative incremental backups entitled "Partial Cumulative Incremental Backups Offer Unique Advantages to Customers.
NOTE: Alternative Uses of Terminology Explained
Some vendors may refer to the term “cumulative incremental backup” when describing their level 1, Differential Backup, capability. We use the term more generally to describe the behavior of a backup at any incremental level (any level except 0) that accumulates data changes since any previous lower level backup (including level 0). Our ability to generate multiple levels of synthetic backups (not just full or differential) provides our customers with a synthetic backup technology that is far more flexible and advanced.
Some vendors may use the term “differential incremental backup” when describing their True incremental Backup capability. We believe this terminology to be confusing, especially when used in conjunction with the term differential backup, which is also considered a form of incremental backup. Additionally, some vendors may require the use of several available backup levels to implement differential incremental backup. For example, levels 4 through 9 may be needed to configure differential incremental backups on a Monday through Saturday schedule. With only three remaining non-zero backup levels, this may limit the number of ways that other lower level backups can be configured. Our True incremental Backup is implemented as a single PCI Backup level and any number of backup levels that may be configured with TiBS.
Three Types of Partial Cumulative Incremental Backup
Direct Partial-Cumulative Incremental: A type of Partial Cumulative Incremental Backup that backs up Primary Storage on a target system to directly attached Secondary Storage on the target system.
Network Partial-Cumulative Incremental: A type of Partial Cumulative Incremental Backup that backs up Primary Storage on a target system over a network to a Secondary Storage.
Synthetic Partial-Cumulative Incremental: A special type of Partial Cumulative Incremental that will consolidate some or all of the Backup Volumes that have been created since the most recent backup at level n or lower on the Backup System. This process is performed by a Backup System with no interaction with the Primary Storage on the target system. The resulting backup volume contains the same data as one that would have been taken from the target system for that period of time.
Additional Backup Volume Resources
Learn About the True incremental Backup System for Enterprise Centralized Network Backup
Three versions of the True incremental Backup System are available. All three versions employ synthetic backup consolidation technology to reduce the load on backup clients and networks. All three versions also have no per seat charges! Learn More ...