> On Fri, 19 Sep 2008 13:50:39 +0000, r wrote:

>> On 2008-09-19, Douglas Mayne wrote:

>

>> You gave me a good tip about doing disks images and restore them via
>> live cd.
>> But, just one question. My root ( / ) is 60 GB, just 6/7 GB are used.
>> If I make a disk image
>> ( for example 'dd if=/dev/sda2 of=/mnt/disco_d/backup_image' )
>> how much it will be the size ? ( 60 GB or 6/7 GB )

>
> All things being equal, an image made that way will consume 60G. There is
> one trick* which can make the image as compressible as possible, though.
> You could create a large file filled with zeroes which uses almost all of
> the space in advance. Then when it is backed up, that zeroed space will
> be easily compressible:
>
> # dd if=/dev/sda2 | gzip >/mnt/disco_d/sda2.img.gz
>
> Other tools are required to avoid zeroing space to minimize the backup to
> the space in use. That is one of the reasons that "one size does not fit
> all," and that other tools exist which have more finesse than dd. As tools
> go, dd is a sledgehammer; tar is a framing hammer. The other tools I
> previously mentioned work better to capture the disk space actually in
> use. Extra care must be taken with the tools you choose because the image
> may not be complete, for whatever reason. For example, tar doesn't
> capture extended file attributes and file acls. These can be backed
> up separately, though, and saved along with the backup. (getfacl,
> getfattr). Depending on which filesystem you are using, there can be
> specialized backup tools; for example, xfs has xfsdump. But for
> simplicity, I often stick with simple tar/gzip backups. The other
> thing which is not captured with this method is the bootloader specifics.
> That must be fixed up separately at restore.

>
> * May not work in advanced filesystems which see you are writing zero and
> create it "sparsely."
>
> --
> Douglas Mayne