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Why are my BRU Archives Larger than the data being backed up?

Views: 8659
Votes: 4
Posted: 10 Aug, 2009

Question

When I perform a backup of data on the system, the resulting BRU archive is larger than the total of the data selected for backup.  Is something wrong with my filesystem?

Answer

Unlike a simple copy, BRU keeps track of data that is normally maintained by the filesystem and not included in normal file size information.  Additionally, BRU tracks other data about files and folders that relate to the specifics of a given operating system's requirements for handling that file that are also not displayed when you examine a file's size.

Finally, BRU maintains multiple entries for much of this "metadata" to provide for the highest level of recoverability of the data written to a BRU archive.

When weighing the difference between the capacity required by BRU for archival against the original filesystem's reported sizes, BRU will use between 12% and 18% of overhead that will use additional space depending upon the number and size of the files processes, the size of the BRU I/O buffer (blocksize), and the type of device used to store the archive.

For safety, use these examples as guideline averages:

Data Backed Up BRU Archive Size
10GB 11.8GB
100GB 118GB
1TB  1.18TB
10TB 11.8TB

 

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