Proper readme

This commit is contained in:
Dennis Schwerdel 2017-04-06 12:12:49 +02:00
parent 1dd4878b4c
commit 7b79456ec3
1 changed files with 62 additions and 104 deletions

View File

@ -1,18 +1,40 @@
# ZVault Backup solution
zVault is a highly efficient deduplicating backup solution that supports
client-side encryption, compression and remote storage of backup data.
## Goals / Features
## Main Features
### Space efficient storage
Each file is split into a number of chunks. Content-defined chunking and chunk
fingerprints make sure that each chunk is only stored once. The chunking
algorithm is designed so that small changes to a file only change a few chunks
and leave most chunks unchanged. Multiple backups of the same data set will only
take up the space of one copy.
### Space-efficient storage with deduplication
The backup data is split into chunks. Fingerprints make sure that each chunk is
only stored once. The chunking algorithm is designed so that small changes to a
file only change a few chunks and leave most chunks unchanged.
The deduplication in zVault is able to reuse existing data no matter whether a
file is modified, stored again under a different name, renamed or moved to
different folder.
Multiple backups of the same data set will only take up the space of one copy.
That makes it possible to store daily backups without much overhead as backups
with only small changes do not take up much space.
The chunks are combined into bundles. Each bundle holds chunks up to a maximum
data size and is compressed as a whole to save space ("solid archive").
Also multiple machines can share the same remote backup location and reuse the
data of each others for deduplication.
### Performance
High backup speed is a major design goal of zVault. Therefore is uses different
techniques to reach extremely fast backup speeds.
All used algorithms are hand-selected and optimized for speed.
Unmodified files are detected by comparing them to the last backup which makes
it possible to skip most of the files in regular usage.
A blazingly fast memory-mapped hash table tracks the fingerprints of all known
chunks so that chunks that are already in the repository can be skipped quickly.
In a general use case with a Linux system and a home folder of 50 GiB, backup
runs usually take between 1 and 2 minutes.
### Independent backups
All backups share common data in form of chunks but are independent on a higher
@ -23,80 +45,45 @@ Other backup solutions use differential backups organized in chains. This makes
those backups dependent on previous backups in the chain, so that those backups
can not be deleted. Also, restoring chained backups is much less efficient.
### Fast backup runs
* Only adding changed files
* In-Memory Hashtable
### Backup verification
* Bundles verification
* Index verification
* File structure verification
## Configuration options
There are several configuration options with trade-offs attached so these are
exposed to users.
### Chunker algorithm
The chunker algorithm is responsible for splitting files into chunks in a way
that survives small changes to the file so that small changes still yield
many matching chunks. The quality of the algorithm affects the deduplication
rate and its speed affects the backup speed.
There are 3 algorithms to choose from:
The **Rabin chunker** is a very common algorithm with a good quality but a
mediocre speed (about 350 MB/s).
The **AE chunker** is a novel approach that can reach very high speeds
(over 750 MB/s) but at a cost of quality.
The **FastCDC** algorithm has a slightly higher quality than the Rabin chunker
and is quite fast (about 550 MB/s).
The recommendation is **FastCDC**.
### Chunk size
The chunk size determines the memory usage during backup runs. For every chunk
in the backup repository, 24 bytes of memory are needed. That means that for
every GiB stored in the repository the following amount of memory is needed:
- 8 KiB chunks => 3 MiB / GiB
- 16 KiB chunks => 1.5 MiB / GiB
- 32 KiB chunks => 750 KiB / GiB
- 64 KiB chunks => 375 KiB / GiB
On the other hand, bigger chunks reduce the deduplication efficiency. Even small
changes of only one byte will result in at least one complete chunk changing.
### Hash algorithm
Recommended: Blake2
### Bundle size
10 M
25 M
100 M
Recommended: 25 MiB
### Data encryption
The backup data can be protected by modern and fast encryption methods on the
client before storing it remotely.
### Compression
The backup data can be compressed to save even more space than by deduplication
alone. Users can choose between zlib (medium speed and compression),
lz4 (very fast, lower compression), brotli (medium speed, good compression), and
lzma (quite slow but amazing compression).
Recommended: Brotli/2-7
### Remote backup storage
zVault supports off-site backups via mounted filesystems. Backups can be stored
on any remote storage that can be mounted as a filesystem:
- SMB / Windows shares
- SSH (via sshfs)
- FTP (via curlftpfs)
- Google Drive (via rclone)
- Amazon S3 (via rclone)
- Openstack Swift / Rackspace cloud files / Memset Memstore (via rclone)
- Dropbox (via rclone)
- Google Cloud Storage (via rclone)
- Amazon Drive (via rclone)
- Microsoft OneDrive (via rclone)
- Hubic (via rclone)
- Backblaze B2 (via rclone)
- Yandex Disk (via rclone)
- ... (potentially many more)
### Backup verification
For long-term storage of backups it is important to check backups regularly.
zVault offers a simple way to verify the integrity of backups.
## Design
### Mount backups as filesystems
Backups can be mounted as a user-space filesystem to investigate and restore
their contents. Once mounted, graphical programs like file managers can be used
to work on the backup data and find the needed files.
### Semantic Versioning
zVault sticks to the semantic versioning scheme. In its current pre-1.0 stage
this has the following implications:
- Even now the repository format is considered pretty stable. All future
@ -105,32 +92,3 @@ this has the following implications:
- The CLI might see breaking changes but at least it is guaranteed that calls
that are currently non-destructive will not become destructive in the future.
Running todays commands on a future version will not cause any harm.
### Packaging
- Included works
- Proper manpage
### Core functionality
- Recompress & combine bundles
### CLI functionality
- list --tree
### Other
- Stability
- Tests & benchmarks
- Chunker
- Index
- BundleDB
- Bundle map
- Config files
- Backup files
- Backup
- Prune
- Vacuum
- Documentation
- All file formats
- Design