Gentoo Archives: gentoo-user

From: Rich Freeman <rich0@g.o>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] backing up a partition
Date: Fri, 24 Aug 2018 12:53:56
In Reply to: Re: [gentoo-user] backing up a partition by Mick
1 On Fri, Aug 24, 2018 at 6:09 AM Mick <michaelkintzios@×××××.com> wrote:
2 >
3 > However, you may prefer to use clonezilla instead of dd. The dd command will
4 > copy each and every bit and byte of the partition whether it has data on it or
5 > not. It is not particularly efficient. Clonezilla will perform better at
6 > this task.
7 >
8 > Personally, I would only keep a back up of the filesystem contents with e.g.
9 > rsync, and reformat the partition and restore its contents in the case of a
10 > disaster recovery scenario.
12 Just to summarize the sorts of options you have:
14 dd = bit level copy. Output is the size of the partition, period,
15 though you could compress the output by piping it into a compression
16 utility/etc. Restored partition is identical to original, including
17 unallocated space, file fragmentation, etc.
19 clonezilla/partimage/etc = sparse bit level copy. Output is the size
20 of all blocks that contain useful data, and can be further compressed.
21 Restored partition will contain zeros in the place of free space, but
22 will still preserve file fragmentation, special filesystem features,
23 etc. Basically these tools operate like dd at a block level, but they
24 first identify which blocks are used/unused. Savings is minimal for a
25 full filesystem, and substantial for a near-empty one. These tools
26 will fall back to dd if they can't identify free space, and can
27 support a wider variety of filesystems quickly because they don't have
28 to be able to mount/read the filesystem, just figure out which blocks
29 matter. I'll also note that with clonezilla you get a fairly nice
30 all-in-one bootable image that can store these images remotely via
31 ssh/samba/etc, which makes restoring images onto bare metal very easy.
33 tar/rsync/etc = file level copy. Output is the logical size of all
34 the files on the filesystem. Restore partition will only contain file
35 contents - details like fragmentation, trailing unused space in
36 blocks, unused space in general, or many filesystem-specific features
37 like snapshots/etc will NOT be preserved. On the other hand it is
38 trivial to restore this data to any filesystem of any type of any
39 sufficient size. The other solutions make resizing or changing
40 filesystems more-or-less impossible unless you can mount the image
41 files and then do a subsequent file-level copy (which is no different
42 than doing a file level copy in the first place).
44 I'd toss in one other general category:
46 dump/send/etc - filesystem-specific serializing tools. The tools are
47 specific to the filesystem, so you can't just point them at a whole
48 hard drive with varying partition types like you can with clonezilla.
49 They may or may not reproduce details like fragmentation, but they
50 will efficiently store the actual data and will reproduce all
51 filesystem-specific features (snapshots, special attributes, etc).
52 They may also contain features that make them more efficient
53 (especially for incremental backups) because they can use an algorithm
54 suited for the low-level data structures employed by the filesystem,
55 instead of doing scanning at the file/directory level. For example,
56 it could just read all the metadata on the disk sequentially as it is
57 physically stored on the disk, instead of traversing it from root down
58 to leaf in the directory hierarchy which could result in lots of
59 seeks. Filesystems like btrfs/zfs have data structures that make it
60 VERY efficient to compare two related snapshots and find just the
61 differences between them, including differences of one block in the
62 middle of a large file without having to read the whole file.
63 Restoration usually is flexible with regard to filesystem size, but
64 not type. That is, if you have a 100GB filesystem with 20GB of data,
65 you could restore it to a 30GB filesystem of the same type, but not
66 one of a different type as with tar.
68 The best solution for you obviously depends on your needs. I try to
69 go with the last category in general as it is far more efficient.
70 But, clonezilla is my general tool for replicating whole systems/etc
71 since it does that so well and works with anything. For partial
72 backups of high-value data I use duplicity, which is file-level (and
73 supports various cloud/etc options for storage).
75 --
76 Rich


Subject Author
Re: [gentoo-user] backing up a partition Bill Kenworthy <billk@×××××××××.au>