Supported Backup Data
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    Supported Backup Data

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    Article summary

    This article answers the question, "What does Backblaze back up?" Backblaze backs up all of your data across all of the user profiles that are on your computer as soon as you install the client.

    Backblaze believes that you do not need to worry whether you selected all of the files that you care about, put any files in a different location on your computer, or added new files that may not be included in your online backup. Therefore, Backblaze automatically selects all of your data.

    Modified Files

    If a file that was already uploaded is modified, Backblaze uploads the delta, or the part that was changed.

    However, if the file is over 100 MB, the file is broken into 10 MB chunks. If the file has data added only to the end of the file, only the last chunk is re-uploaded. If data is entered into the middle of the file, every chunk after that point is re-uploaded because the data has been pushed back and each of the following blocks changed.

    Boot Drives

    By default, your boot drive C: (Windows) or Macintosh HD (Mac) are always selected for your backup to run properly. If you attempt to disable this drive, a warning message is displayed.

    File Size

    There is no limit to the file sizes that you can back up. Backblaze is truly unlimited, but you should keep your computer and network limitations in mind.

    A large number of files can use up a lot of your system resources. As part of the backup process, Backblaze runs a checksum against each file before uploading it. This requires the entire bzfileids file to be loaded into RAM. The bzfileids file contains a list of all of your files. If you have an extraordinarily large number of files, this could cause Backblaze to use a significant amount of RAM. After a while you may receive a "bzfileids.dat file is too large" error. Backblaze can back up only as fast as your connection allows. 

    You may want to request a USB Restore Drive for large restores.

    You can lower the default value of "No Limit" in your exclusion settings. Click here for Mac instructions. Click here for Windows instructions.

    Multiple User Accounts on a Computer

    On both Mac OS X and Windows, Backblaze installs as a background service, called a daemon. As such, it can back up all of the local user accounts that are on your computer; not just the account that you were logged into during the client installation.

    Temporary Storage

    Backblaze does not support the inclusion of removable media in backups, including CDs, DVDs, SD cards, ZIP disks, floppy disks, and other similar storage devices.

    To back up this data, you must move it to an internal drive or a drive that is connected using a USB drive, Firewire, or Thunderbolt.

    Flash keys may help back up temporary storage depending on its designation. If it is designated by your operating system as temporary storage that cannot be changed, then Backblaze is unable to back up this drive. You must copy these files to another backed-up drive to include them in your backup.

    Mac OS Packages

    A package is a directory that looks like a single file in Finder. Since a package is just a special folder, Backblaze sees it as a folder and backs it up as such. For more information, click here.

    Email Files

    Backblaze backs up your email if it is locally stored on your computer. Email applications like Outlook, Outlook Express, Apple Mail, Thunderbird, Eudora, and Windows Live Mail are backed up.

    Backblaze backs up only the difference to the email database (for example, PST, DBX, and database files) and does not re-upload the entire email database.

    However, Backblaze cannot back up files while they are in use or locked by other applications. If you commonly leave your mail application open, close it at least daily to ensure that the file is regularly backed up.


    Backblaze uses a lossless compression method (ZIP). This means that when you restore your files, they are bit-for-bit identical to the originals. Backblaze does not use any lossy compression such as JPEG so that your photo quality never degrades when the files are compressed.

    Library Folders

    By default, Backblaze backs up the Mac user-level library for each user at /Users/yourusername/Library or ~/Library. Backblaze does not back up the top-level library folder at /Library.

    The user-level library contains items like settings and preferences, mail, browser bookmarks, calendars, address book data, and widgets. A significant amount of unique user data is stored in that folder.

    The user-level Library may be hidden depending on your version of Mac OS X.

    The top-level Library folder contains primarily non-unique operating system files and caches. Excluding this folder makes your backup complete faster and uses less bandwidth.

    The data in /Library is recreated when an operating system is installed and applications are reinstalled.

    If you have data in the top-level Library folder that you want to back up, make a copy of it to a location that Backblaze does back up. There is no way to override /Library to include it in your backup.

    Disk Encryption Software

    Backblaze backs up Mac FileVault files and sparse bundles when your computer is unlocked and Mac FileVault is enabled.

    Connected Drives

    Backblaze backs up USB and Firewire hard drives and internal drives that are connected at the time of the install or added later in settings.

    Flash Drives

    A flash drive (also known as a thumb drive or memory stick) can potentially be backed up as a connected drive, depending on how your operating system views the drive. On Windows, if a plugged-in flash drive appears as removable media, then Computer Backup cannot back up the drive. On the other hand, if the flash drive appears as a hard drive, then Computer Backup can back up the drive.

    The Computer Backup software cannot control how a flash drive is viewed by the operating system. That behavior is determined by the operating system and the flash drive manufacturer.


    Backblaze organizes your online backup around the concept of "top-level drives." When you install the Backblaze client on your computer, it scans for any permanently attached hard drives (not network drives or removable media like CDs or flash drives) to back up. To add or remove an external hard drive, click here.

    Archived Files

    Backblaze Computer Backup is designed to protect the files that you care about. Backblaze retains a remote backup of any file that exists on your computer. Additionally, Backblaze retains multiple versions of that file for up to 30 days by default. However, Backblaze Computer Backup is not designed as an additional storage system. Therefore, you should not upload your external hard drive to Backblaze Computer Backup and then delete the data off your drive because those files are deleted from the Backblaze servers as well. 

    Additionally, Backblaze must continue running on your computer to perform self-maintenance and maintain the correct mirror copy of your files in the Backblaze data center on an ongoing basis. If, for any reason, the Backblaze data center does not hear from your computer after six months, the backup copy of your data may be removed from the data center and your account is subject to cancellation.

    Backblaze has an extended version history feature that allows you to bypass the 30-day limit. You can choose one year of retention or forever. For more information, see Version History.

    Thumb Drives

    On a Windows operating system, if the drive appears under removable media and not hard disk drives, then Backblaze does not back up these drives. If it does appear under hard disk drives, then Backblaze does back up the thumb drive.

    The area where the drive is added, hard disk drives or removable media, is dictated by the Windows operating system. The Backblaze client does not have any say as to how the drive is mounted and works only with the information that the operating system provides.


    To save your bandwidth and data center disk space, Backblaze does not back up your operating system, application files, empty folders or directories, or temporary internet files that are transient. You can see these exclusions by navigating to the Backblaze control panel, clicking Settings, and selecting the Exclusions tab. Some of these excluded files include: ISO (Disk Images), VMC VHD VMSN (Virtual Drives), SYS (System Configuration & Drivers), and EXE (Application Files). You can remove all of these file types from this area. For example, to back up an ISO, remove .iso from the list.

    Backblaze also does not include backup products like Time Machine and Retrospect RDB. Other excluded files include podcasts in iTunes, thumbnails, and caches from iPhoto, Aperture, or Lightroom. Additionally, aliases, Libraries, Reparse Points, Shortcuts, Symlinks, and folders that are shared from another computer are not included in the backup.

    Exclusions apply to all drives, meaning that all of the folders and files with the same name are excluded across all drives. For example, since C:\Windows\ is excluded, then G:\Windows\ is also excluded.

    Network Drives and NAS

    Network-mounted drives, network-attached storage (NAS) devices, remotely mounted computers or volumes, and shared volumes are currently excluded from Backblaze Computer Backup. However, you can back up network drives using Backblaze B2 Cloud Storage.

    Time Machine Drives

    To avoid duplicating data, Backblaze does not back up any drive that contains Time Machine data.

    If you want to back up a Time Machine drive to Backblaze, you have two options:

    Data Seeding

    Backblaze is not able to seed backups. Backblaze can accept only data that is transmitted from your computer and drives to Backblaze using the internet.

    If you have a very large data set, you can look into the Fireball Program. This program works along with Backblaze B2 Cloud Storage. For more details, see Backblaze Fireball Program.

    Photos, iPhoto, Aperture, and Lightroom use library bundles that Backblaze backs up at any size.

    Symbolic Links

    A symbolic link is a file whose purpose is to point to a file or directory by specifying a path thereto. Backblaze does not back up symbolic links.

    Volume Shadow Copy

    Backblaze does not support Volume Shadow Copy. When a file is locked or "in use," Backblaze is not able to read it and creates a temporary copy of the file that is needed for the upload process. 

    If Backblaze attempts to upload a file that is in use, the file is skipped until the next attempt to upload (approximately one hour).

    You can check the files that are being skipped by opening the Backblaze client Reports (Mac) or Issues (Windows). This provides a list of the files that Backblaze skipped and attempts to back up again later. If the file is open in another program, it shows as Temporary File Busy.


    Backblaze does not officially support Voiceover. If you have issues preparing restores or performing any other operations on your account, contact the Support team.

    Windows.old Directories

    Backblaze does not back up any directory at the root level named Windows.old. This file has a special connotation from Microsoft; it is the name of the folder that is used after an upgrade to Windows.

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