It depends on whether the disk image is a full disk image, or just a partition.
Washing the partition(s)
If the disk is in good working condition, you will get better compression if you wash the empty space on the disk with zeros. If the disk is failing, skip this step.
If you’re imaging an entire disk then you will want to wash each of the partitions on the disk.
CAUTION: Be careful, you want to set the
of to a file in the mounted partition, NOT THE PARTITION ITSELF!
mkdir image_source sudo mount /dev/sda1 image_source dd if=/dev/zero of=image_source/wash.tmp bs=4M rm image_source/wash.tmp sudo umount image_source
Making a Partition Image
mkdir image sudo dd if=/dev/sda1 of=image/sda1_backup.img bs=4M
sda is the name of the device, and
1 is the partition number. Adjust accordingly for your system if you want to image a different device or partition.
Making a Whole Disk Image
mkdir image sudo dd if=/dev/sda of=image/sda_backup.img bs=4M
sda is the name of the device. Adjust accordingly for your system if you want to image a different device.
Make a “squashfs” image that contains the full uncompressed image.
sudo apt-get install squashfs-tools mksquashfs image squash.img
To avoid making a separate temporary file the full size of the disk, you can stream into a squashfs image.
mkdir empty-dir mksquashfs empty-dir squash.img -p 'sda_backup.img f 444 root root dd if=/dev/sda bs=4M'
Mounting a compressed partition image
First mount the squashfs image, then mount the partition image stored in the mounted squashfs image.
mkdir squash_mount sudo mount squash.img squash_mount
Now you have the compressed image mounted, mount the image itself (that is inside the squashfs image)
mkdir compressed_image sudo mount squash_mount/sda1_backup.img compressed_image
Now your image is mounted under
EDIT: If you wanted to simply restore the disk image onto a partition at this point (instead of mounting it to browse/read the contents), just
dd the image at
squash_mount/sda1_backup.img onto the destination instead of doing
Mounting a compressed full disk image
This requires you to use a package called kpartx. kpartx allows you to mount individual partitions in a full disk image.
sudo apt-get install kpartx
First, mount your squashed partition that contains the full disk image
mkdir compressed_image sudo mount squash.img compressed_image
Now you need to create devices for each of the partitions in the full disk image:
sudo kpartx -a compressed_image/sda_backup.img
This will create devices for the partitions in the full disk image at
/dev/mapper/loopNpP where N is the number assigned for the loopback device, and P is the partition number. For example:
Now you have a way to mount the individual partitions in the full disk image:
mkdir fulldisk_part1 sudo mount /dev/mapper/loop0p1 fulldisk_part1
root@srv1:/backup# archivemount windows-2003-S.gz /target/ Unrecognized archive format root@srv1:/backup# archivemount -o formatraw windows-2003-S.gz /target/ Calculating uncompressed file size. Please wait. root@srv1:/backup# ls /target/ data root@srv1:/backup# file /target/data /target/data: DOS/MBR boot sector; partition 1 : ID=0x7, start-CHS (0x0,1,1), end-CHS (0x3ff,254,63), startsector 63, 58717512 sectors, extended partition table (last)
archivemount is a FUSE-based file system for Unix variants, including Linux. Its purpose is to mount archives (i.e. tar, tar.gz, etc.) to a mount point where it can be read from or written to as with any other file system. This makes accessing the contents of the archive, which may be compressed, transparent to other programs, without decompressing them.
After mounting archive you can use it contents like regular file. Maybe get partition table, or convert, mount image with qemu tools.
squashfs useful for booting from image, but much complex for backuping.
If the image is read-only you can also use nbdkit (man page) and its xz plugin (xz should provide better compression and random access times than gzip).
Create the compressed partition image
dd if=/dev/sda1 bs=16M | xz -9 --block-size=16MiB - > sda1.img.xz
--block-size option of 16 MiB should provide good random access performance.
Note: you may use alternative xz compression programs such as pixz which provides parallel compression, just make sure it splits the output in multiple small blocks, otherwise nbdkit has to decompress a lot of data. For example as of September 2015, pxz does not support this.
Serve it with nbdkit
nbdkit --no-fork --user nobody --group nobody -i 127.0.0.1 xz file=sda1.img.xz
Connect to the NBD server
nbd-client 127.0.0.1 10809 /dev/nbd0 -nofork
Mount it read-only
mount -o ro /dev/nbd0 sda1
umount /dev/nbd0 nbd-client -d /dev/nbd0
Stop nbdkit by pressing Ctrl+C (or with kill).