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doc: Clarify storage ID

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Alexander Neumann 2015-05-04 20:39:07 +02:00
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doc/Design.md
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@ -21,17 +21,16 @@ been backed up at some point in time. The state here means the content and meta
data like the name and modification time for the file or the directory and its
contents.
*Storage ID*: A storage ID is the hash of the content of a file stored in the
*Storage ID*: A storage ID is the SHA-256 hash of the content stored in the
repository. This ID is needed in order to load the file from the repository.
The storage hash is the SHA-256 hash of the content.
Repository Format
=================
All data is stored in a restic repository. A repository is able to store data
of several different types, which can later be requested based on an ID. This
so-called "storage ID" is the hash (SHA-256) of the content of a file. All
files in a repository are only written once and never modified afterwards. This
so-called "storage ID" is the SHA-256 hash of the content of a file. All files
in a repository are only written once and never modified afterwards. This
allows accessing and even writing to the repository with multiple clients in
parallel. Only the delete operation removes data from the repository.
@ -40,7 +39,7 @@ directories and files. Such repositories can be accessed locally on the same
system or via the integrated SFTP client. The directory layout is the same for
both access methods. This repository type is described in the following.
Repositories consists of several directories and a file called `config`. For
Repositories consist of several directories and a file called `config`. For
all other files stored in the repository, the name for the file is the lower
case hexadecimal representation of the storage ID, which is the SHA-256 hash of
the file's contents. This allows easily checking all files for accidental
@ -269,9 +268,8 @@ Snapshots
A snapshots represents a directory with all files and sub-directories at a
given point in time. For each backup that is made, a new snapshot is created. A
snapshot is a JSON document that is stored in an encrypted file below the
directory `snapshots` in the repository. The filename is the SHA-256 hash of
the (encrypted) contents. This string is unique and used within restic to
uniquely identify a snapshot.
directory `snapshots` in the repository. The filename is the storage ID. This
string is unique and used within restic to uniquely identify a snapshot.
The command `restic cat snapshot` can be used as follows to decrypt and
pretty-print the contents of a snapshot file:
@ -296,7 +294,7 @@ hash. Before saving, each file is split into variable sized Blobs of data. The
SHA-256 hashes of all Blobs are saved in an ordered list which then represents
the content of the file.
In order to relate these plain text hashes to the actual location within a Pack
In order to relate these plaintext hashes to the actual location within a Pack
file , an index is used. If the index is not available, the header of all data
Blobs can be read.
@ -367,9 +365,9 @@ This tree contains a file entry. This time, the `subtree` field is not present
and the `content` field contains a list with one plain text SHA-256 hash.
The command `restic cat data` can be used to extract and decrypt data given a
storage hash, e.g. for the data mentioned above:
plaintext ID, e.g. for the data mentioned above:
$ restic -r /tmp/restic-repo cat blob 00634c46e5f7c055c341acd1201cf8289cabe769f991d6e350f8cd8ce2a52ac3 | sha256sum
$ restic -r /tmp/restic-repo cat blob 50f77b3b4291e8411a027b9f9b9e64658181cc676ce6ba9958b95f268cb1109d | sha256sum
enter password for repository:
50f77b3b4291e8411a027b9f9b9e64658181cc676ce6ba9958b95f268cb1109d -