File Sizes

By default, Backblaze does not have file size restrictions. The Backblaze Computer Backup client uploads files sequentially from smallest to largest. This allows the smallest files on each system to be uploaded in batches, significantly improving upload rates due to reductions in overhead. 

Large Files

Files that are larger than 100 MB are parsed into 10 MB chunks for transmission. If you have a 10 GB video file that you want to back up, the file is copied in 10 MB chunks to a temporary Backblaze folder that is 1x the space of the file. Each chunk is checksummed, packaged, and prepared for transfer (up to 0.1x the space of the original file). Each chunk is transmitted, and after all of the pieces are transmitted and confirmation is received from the servers, the chunks are deleted, and the next file is processed.

If you have an external drive, you can set a temporary data drive in the Backblaze settings to one of your external drives that has ample space. This means that when that external drive is connected and available, Backblaze sets its temporary folder to that external drive and performs its chunking operations there avoiding your internal drive.

Versioning of large files is limited to one every 48 hours. If a large file is changed multiple times throughout a several-day period, only one version of that file is uploaded every 48 hours.

If you have extremely large files that are slowing down or clogging your backup, consider excluding the large files from a backup.

• Mac Exclusions
• Windows Exclusions

Calculating File Sizes

If you use a Mac computer, you may notice that the size of a file is reported differently on your Mac than how it is reported when viewed in the Backblaze web console.

Here are three typical examples:

• A file appears to be 100 KB on your Mac, but in the file browser, it appears to be 97.66 KB.
• A file appears to be 100 MB on your Mac, but in the file browser, it appears to be 95.37 MB.
• A file appears to be 1 GB on your Mac, but in the file browser, it appears to be 953.67 MB.

There are different methods for calculating the size of a file that result in a different reported file size depending on the operating system that you use. Mac OS X 10.6 (Snow Leopard) and newer calculates file size using decimal (base 10) math. While binary (base 2) math is used by the Computer Backup file browser, Windows, and Mac OS X 10.5 (Leopard) and earlier.

When calculating file size using decimal (base 10) math:

• 1 KB is 1,000 bytes
• 1 MB is 1,000,000 bytes or 1,000 KB
• 1 GB is 1,000,000,000 bytes or 1,000 MB

When calculating file size using binary (base 2) math:

• 1 KB is 1,024 bytes
• 1 MB is 1,048,576 bytes or 1,024 KB
• 1 GB is 1,073,741,824 bytes or 1,024 MB

Files are backed up and restored with actual bytes, and they are not modified in any way. KB, MB, GB are simply terms that are displayed to avoid large numbers of raw bytes. For example, it is easier to read "1.5 GB" than "1610612736 bytes."

If you use Mac OS X 10.6 (Snow Leopard) or newer and you want to see how your file size compares with the size that is reported in Computer Backup, you can convert between the base 10 and base 2 number systems as follows:

• Take the number of KBs that your Mac reports, and multiply by 0.9765 to get the number of KBs that Computer Backup will report.
• Take the number of MBs that your Mac reports, and multiply by 0.9536 to get the number of MBs that Computer Backup will report.
• Take the number of GBs that your Mac reports, and multiply by 0.9313 to get the number of GBs that Computer Backup will report.

Regardless of which method is used to calculate a file's size, the file data remains unchanged. When you download a file from Computer Backup and view it on your computer, it displays the correct file size, no matter what operating system you use.

For more information, view the following articles:

• Storage Capacity on Apple Devices
• Byte Converter
• Prefixes for Binary Multiples