odarchive 0.1.0
Convert file systems to archiveable ISO files
License: MIT license
Keywords: cdrom,dvd,bdrom,archive,odarchive

# odarchive

Optical disc archiving - converting file systems to sets of ISO files and back.  It is meant for archiving
information to optical disc for long term data storage.   


This readme is broken into sections:

- Command line usage
- Technical description
- Software description
- Future Enhancements
- License (MIT)

# Command line usage

Summary of commands, see below for commandline options.    

Commands  | Comment
----------|---------- 
init      | Creates a new catalogue 
write_iso | write out an iso  
archive   |
segment   | split archive into segments

## odarchive create_db drive_path

Creates a database catalogue.json in current working directory from
files in drive_path

## odarchive plan_iso size
Enriches the database to plan building ISO with a maximum size of n
bytes or using

- 'cd'     = 700MB
- 'dvd'    = 4.7GB
- 'bd' = 25GB
- 'bluray' = 25GB
- 'bd-dl' = 50GB
- 'bd-xl' = 100GB
- 'bd-xx' = 128GB

## odarchive num_isos
*Planned* Return number of isos required

## odarchive create_iso n
Default for n is 0 (numbering from Zero)


# Technical Description

## Segmentation
When a catalogue is created for the first time it is not segmented.
Segmenting refers to writing out a single disc which has smaller
capacity than the total archive.

## File name
This services is planned to work from supplied USB drives.
The internal file name is a UDF Abolute Path. It is an absolute path
  so that if the name of the Data directory changes this wonâ€™t make a
  difference when combining discs with different naming conventions.

User case history: I want to backup some critical files first eg my own
Photgraphs and video and then other files The deeper the file system on
the USB the better the result will be

## disc directory layout

```
/Data + All data files catalogue.json #
README.MD
```

## Json file format

JsonFile = HeadingSection \*FileDefinition
HeadingSection = Version
FileDefinition = Hash FileNameList Mtime Size

Max. filename length 255 bytes (path 1023 bytes)

Example::
```
    {
        "version": 1,
        "files" :  {
            "Hash1": {
                filenames : {
                    "data/first.html" : null,
                    "data/first_copy.html" : null,
                }
                size : 21,
                mtime : ??
            },
            "Hash2": {
                filenames : {
                    "data/second.txt" : null,
                }
            size : 22,
            mtime : ?? },
        }
    }
```
# Software Structure

### Object Structure

The main objects is an Archive object.

This has two main sub objects:

- a File_db
- a hash_file_db

The file_db is a temporary structure which is derived from walking the file system.
The hash_file_db is then derived from that by taking the hashes of all those files and then building 
a database of each unique file.  This then shows the multiple location of where the file is stored.

### File Structure
This is one module: odarchive.


This has three parts:

This has three top level modules: 
 - ``archive.py`` which handles the
archive 
- ``odarchive_cli.py`` which puts a command line wrapper around
the archive code. 
- a ``_version.py`` which holds the version number
constants for both pypy and the code

The archive code is the main code and 4 sub files: - ``consts.py``
General constants - ``file_db.py`` handles a file database - ``hash_db``
extends the file database to include a database of hashentries -
``hash_file_entry.py`` creating hashes for single files

There is a distinct order in which things must happen:

-Scan the file and build a file database.
-Create a hash tables

## Unique ID's

There is a job_id which is created at the start of a job.  This should be unique and last the life
time of the job.  There is also a guid with the catalogue, this changes every time it is saved/changed and 
is like the version of the archive.

## Limitations

### Saving an archive
When an archive is saved it is put into a catalogue.json file.  This is only possible once all the hashes
for the files have been created as the format is indexed the file hash.

Temporary work can be saved via the save_as_dill method.

## Inspiration

Thanks to M Ruffalo of
https://github.com/mruffalo/hash-db/blob/master/hash_db.py for a lot of
inspiration.

# Future enhancements


### convert a json catalogue into a pickle
Currently when working on a backup plan the data is pickled from command
to command. In order to work with existing cataloges this is what you
need.

### Make a .exe
Create a single exe that will do this job or make an exe that can be
installed via pip.

### Segemented isos into specific size

### Convert catalogue from dictionary to database
At the moment the catalogue database is an in memory dictionary. This
will limit it to about 2 million files per GB of available memory.

### Make a service with feedback on status
Eg archiving Z drive has taken at least an hour and I donâ€™t if working
or crashed.

### Make calculating Hash multi threaded
May work faster

### Add size of catalogue to length of reserved space

### Incremental
- With an old catalogue and drive path create a additional catalog. Can
  be current point in time, eg so not reference files that were deleted.
- This also allows rescanning without making any changes. This should
  also cover the case of multiple single backups being coalesced into a
  bigger backup. You might in large file format decide to backup a
  number of individual files first.

### Split large files

### Make a service as a Glacier replacement.

Eg rerun and post changes via web

### Make read only cached drive

robot plus discs 600 discs = 15TB

### Calculate directory size when segmenting

At the moment a fixed directory size is added to each entry

### get_info

Add JsON alternative to returned data

### Make Platinum discs

GBP16 a g SG 19 1u 12cm area = 0.012 a 1u coat costs about GBP4 a disc
However if these had a glass substrate they might have a very long life.
Potentially you could write them naked and then cover them with another
glass slip. Could even write with an electron beam although might be
expensive

### UDF Bridge format
To make the discs more compatible add a ISO 9660 directory structure as
well as the UDF

In order to make the discs more compatible both a UDF and a ISO 9660
directory structure are output. There are different levels of ISO 9660
structure but I have chosen level 3 as the standard.

The ISO 9660 leads to complications as it is restricted to shorter
directory names and a maximum directory depth of 7. This means the the
conversion from UDF directories to ISO 9660 directories is lossy. From
this it means that you have to implement a lossless scheme (store the
directory mapping as a dictionary) so that you can do multiple backups
on multiple discs and still have a coherent directory structure.


### Adding error correction
The main aim of this is to measure the degradation of the storage media and to know when
the data needs restoring.  In a DRAM this is done all the time - it should also be done on raid drives
to scrub the errors.

# Licensing
Using an MIT license see LICENSE.


V0.0.0 2018-10-04
=================

First release