backy-extract

High-performance, standalone backup restore tool for backy. backy-extract restores a specified backup revision to stdout or a file/block device target.

Usage

1. Pick a backup revision, for example using backy status.
2. Create a restore target, for example with lvm or rbd image.
3. Extract backup: backy-extract /srv/backy/vm/Nym6uacWoXGb8VnbksM3yH /dev/rbd0

Interaction with backy

backy-extract tries to acquire the purge lock before proceeding. So if it does not seem to start, check if there are running backy processes operating on the same backup.

Sparse mode

Block devices are assumed to be zeroed (discarded) before restoring. If this is not the case, invoke backy-extract with --sparse=never.

Compiling

In general, cargo build --release should do the right thing. This application depends on liblzo2 being availabe. If you get compiler/linker errors, try compiling again with export LIBRARY_PATH=/path/to/liblzo2.

A Makefile is supplied to create a statically linked release which should run on virtually every Linux x86_64 system.

FUSE driver (backy-fuse)

backy-fuse provides access to individual revisions via FUSE (filesystem in userspace). This allows to mount backup images and retrieve single files.

Usage

1. Start backy-fuse to access all backups of a given VM via FUSE: backy-fuse -d /srv/backy/vm /mnt/backy-fuse
2. Mount the revision of interest: mount -o ro,loop /mnt/backy-fuse/tAGKE5rrxReggVMtoPSr7 /mnt/restore

When finished, the above stops must be reversed:

1. Unmount loop device: umount /mnt/restore
2. Finish FUSE: fusermount -u /mnt/backy-fuse

Note that in case the image contains a partition table, the loop device must be set up explicitly using for example: losetup -f -P --show /mnt/backy-fuse/tAGKE5rrxReggVMtoPSr7

lostup will create subdevices for each partition, e.g. /dev/loop0p1.

Don't forget to remove the manually created loop devices with losetup -D after use.

Caching

backy-fuse maintains two caches: A read-only cache to speed up read operations and a dirty cache to store pages which have been written to. Both caches have the same size, which may be specified with the -c flag. Note that chunk will spill into the backy directory if the dirty cache gets too full. This is generally not a problem because the next backy purge run will clean it up. However, it is strongly recommended to mount FUSE volumes with the ro flag.

Debugging

Set RUST_LOG=info or even RUST_LOG=debug in the environment for FUSE protocol diagnostics.

Compiling

backy-fuse is not compiled by default due to restricted portability. To compile it, run cargo build --release --features fuse_driver. Note that both liblzo2 and libfuse must be detectable by the linker.

Hacking

Please create issues and submit pull requests at https://github.com/flyingcircusio/backy-extract/.

Author

Contact Christian Kauhaus for questions, suggestions, and bug fixes.