diff --git a/FAQ.md b/FAQ.md index 0dee8085f..4d7224139 100644 --- a/FAQ.md +++ b/FAQ.md @@ -33,6 +33,7 @@ General Public License v2 (GPLv2). See LICENSES directory or go to * [What happens when I remove a backup?](#what-happens-when-i-remove-a-backup) * [How can I exclude cache folders to improve backup speed and reduce storage?](#how-can-i-exclude-cache-folders-to-improve-backup-speed-and-reduce-storage) * [How to use extended filesystem attributes (xattr) to exclude files/directories?](#how-to-use-extended-filesystem-attributes-xattr-to-exclude-filesdirectories) + * [How does Back In Time handle open or changed files during backup?](#how-does-back-in-time-handle-open-or-changed-files-during-backup) - [Restore](#restore) * [After Restore I have duplicates with extension ".backup.20131121"](#after-restore-i-have-duplicates-with-extension-backup20131121) * [Back In Time doesn't find my old backups on my new Computer](#back-in-time-doesnt-find-my-old-backups-on-my-new-computer) @@ -530,6 +531,46 @@ If you encounter clear rules about configuring Samba that it works with _Back In Time_ in a reliable way, please let us know the details. We will than integrate it into the documentation. +## How does _Back in Time_ handle open or changed files during backup? + +**Explanation** + +Back In Time uses rsync to copy the files and directories specified to be +backed up in the configuration. Rsync does not lock any files that are open +or being modified and therefore the backup can be copied in an inconsistent +state. Rsync only reads a file on time when it goes through it and as a result +of this only some changes are captured by rsync. This can affect files such as +logs, browser caches, databases or virtual machine images where inconsistencies +can even lead to data corruption. + +**To reduce this risk, the following approaches can be considered:** + +- **Filesystem snapshots** + If using a filesystem like btrfs and ZFS that has a snapshot function this + can be used together with Back in Time. Filesystem snapshots provide a + read-only copy of a filesystem frozen at a specific point in time, which + ensures data integrity even for open/changing files. Configure Back In Time + to backup from this filesystem's read-only snapshot. + +- **Use exclusions** + If the filesystem does not have filesystem snapshots available, one + solution could be to exclude files that are frequently open or actively + changing. The command `lsof` in GNU/Linux presents open files and the + processes that opened them as a list. Use this list as base for + configuring BIT exclusion list. + +- **Application specific handling** + For applications that opens and modifies files frequently like databases + or virtual machines, specific solutions may be needed. Use the databases + own backup function to create a consistent copy and include that in the + BIT backup. Virtual machines products typically have ability to create + snapshots of their state, that can be included in BIT. + +- **Choose when to perform backup** + Perform backup at times where less files are open, for example at night. + + + # Restore ## After Restore I have duplicates with extension ".backup.20131121"