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One copy is not a backup

In theory backup is a simple process. Copy all files to another device and store it safely and use the copy in an emergency to recover data. But in practice it is not so simple.

The theory

  • What is a backup?

    Preventive making copies of computer files.

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  • Purpose of a backup

    These copies are made to secure data in case the data on the original carrier is lost or damaged.

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  • Types of loss and matching backup methods

    Human errors, are one of the most common causes of data loss. The "accidentally" throwing away or damaging of a file by the user can be solved by making copies of important files on the same disk.

    Device failure, including failure of the hard disk. This can be overcome by an additional backup to disk or a RAID configuration.

    Disasters, such as theft, fire, lightning, power surges and flooding could be overcome by storing backups on other sites.

    Volume and directory damage, caused by viruses and software bugs are often not immediately noticed. Recent backups may already contain a copy of the corrupted data. It is therefore wise to keep several backups over a longer period.

    RAID is not a replacement for backing up your data. A backup is a separate copy of a file, written to another device. A backup should be able to survive even if the original fails. Some storage such as RAID/Drobo devices seem backups but are not.

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The practice

A good backup…

  • Is at least 3 copies.

    In the event of a major disaster is likely that the site copy is lost or corrupted. Dan heeft u nog twee kopieën over. Copy number of two, you can then start to recover, but if it includes an error in the recovery process than you will have to fall back to the third copy to restore the remaining files.

    The above is a simplified representation of reality. Depending on the size and desired recoverability rate, you choose the number of backups for your situation.

    File size

    To properly restore a file you need 100% of the stored information. So with large files there is a greater risk of non recoverability than with a smaller file.

    Recoverability rate

    Each storage medium will sooner or later, show more or less errors. By radiation, dust, physical damage or wear on moving parts for example.

    Manufacturers often give the expected probability of failure as a mean time between failures (MTBF). For example, a hard disk has an MTBF of 1 million hours, that is117 years. In the view of researchers at Carnegie Mellon universities, this theoretical MTBF value is rather optimistic assessed. In practice, failures of hard drives averaged to appear 2 to 5 times more often in common, with peaks to 15 times more often. There are also limitations by specification, including a number of expected non recoverable read errors and a maximum number of load and unload cycles. Then reading a medium requires apparatus such as a disk controller, a power supply and so on. These are all vital components in the circuit, each with their own MTBF value. Each component must work flawlessly separately for the whole chain to function without error, in other words these components form a series circuit, so the value of the overall system MTBF is lower.

    Recoverability rates are not an exact science. But according to the rules of parallel systems adding an extra backup destination reduces the possibility of non-recoverability quadratically.

    Pessimistic failure probability (estimate) for restore of 3MB files with CrashPlan PRO
    Backups¹ Failure probability 1 on … files 1 on …
    1 5‰
    2 0,03‰
    3 0,0001‰
    4 0,0000006‰
    5 0,000000003‰
    Average failure probability (estimate) for restore of 3MB files with CrashPlan PRO
    Backups¹ Failure probability 1 on … files 1 on …
    1 0,3‰
    2 0,00009‰
    3 0,00000003‰
    4 0,000000000008‰
    5 0,000000000000002‰

    ¹ number of available backup copies after a disaster

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  • Is located onsite, offsite and online

    Onsite is the backup on the same spot as that of the protecting data. For fastest backup and restore.

    Offsite is the backup located on a different site than the data to be protected. Your own computer in an adjacent building, on another branch or at the supervisor's home. Protection in the event of an emergency by transporting the copy at the offsite location.

    Online is located in an internet data center. A controlled environment with emergency power, air conditioning, fire extinguishing, security and high speed internet. Faster backup and restore over the internet than offsite.

    CrashPlan PRO provides the only backup solution with the ability to send data to multiple destinations. The choice of locations is unlimited: in the office to the local server via USB or Wi-Fi to an external hard drive or over the Internet to a remote server. Such offsite destination you'll add with the same ease. So you are able to use any computer with an internet connection as a backup destination.

    The best you combine the Pro Backup service with a local destination and an offsite destination.

    Overall system availability and downtime per year in a pessimistic scenario with different SLA's of the own internet combined with 1, 2 and 3 parallel Pro Backup destinations²
    Type of business Own internet connection Pro Backup service
    SLA Availab. Down Availab. Down Availab. Down Availab. Down
    5×8h bronze 95% 18d 93%
    d   95%
    d   95%
    6×12h silver 99,6% 34h 97,9%
    h 99,6%
    h 99,6%
    7×24h gold 99,9% 9h 98,2%
    h 99,9%
    h 99,9%
      platinum 99,95% 4h 98,3%
    h 99,92%
    h 99,95%

    ² These calculations are based on 98.3% availability of each Pro Backup destination. This is not a guarantee.

    Overview of the different options
    Best suited for SMEs with … Number of destinations Most common benefit How to order
    online offsite onsite
    • business DSL/ADSL
    • two connections
    • silver (99,6%) SLA
    quick recovery and less risk standard
    • single internet connection
    • without guarantees/SLA
    • limited budget

    lower costs but more risk advanced 
    • fiber optic connection
    • gold (99,9%) SLA
    • triple connections
    • servers in data centers
        easy and less risk advanced
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  • Is made with two different software applications

    Backup software comes in all shapes and sizes, it can even be included in your operating system. But it is not always suitable for any purpose, such as creating a bootable backup, a real-time backup or an offsite backup. Furthermore software is never error-free and no computer exactly the same. Chances are that a software error in the backup creates a problem.

    Since the CrashPlan PRO software is not suitable for all backup types CrashPlan PRO combines best with bootable backup software for backing up your operating system and with mirror backup software for your data.

    Backup types and the suitability of the CrashPlan PRO software
    Backup method Suitability of CrashPlan PRO
    Mirror No, CrashPlan PRO requires a recovery process
    Compressed mirror Yes
    Real time / Continuous / CDP Yes, via NTFS, Spotlight, inotify
    Offsite Yes
    Bootable No, os x using bless command
    Bare-metal (without operating systeem) No
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  • Starts automatically and runs continuously in the background

    Once you set the CrashPlan PRO software. You specify what you want to backup, how often and to which destinations. You can then close the program. CrashPlan PRO runs as a background process, without you having to worry about. From now on you can not forget.

    The first time the program creates a full backup. Afterwards CrashPlan PRO uses capabilities of your operating system to detect changes. Only new files and changes to existing files are sent. Further CrashPlan PRO exploits available bandwidth and storage capacity by optimally compressing your data before sending and storing.

    For computers with less memory, a less powerful processor, less I/O performance or a slow internet connection, you set yourself which part of your bandwidth and processing power in your presence or absence may be used. This allows you to minimize the impact on the speed of your computer while working.

    Data changes often and probably the most important data is that you are working on right now. The moment a file is changed CrashPlan PRO will be alerted to by the operating system. Thus CrashPlan PRO is able to backup in as little as 1 minute after a change. This means you always have a current backup.

    Backups should be always be performed on a regular basis and before modifying any storage volumes using disk utilities.

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  • Keeps historical versions

    The retention of an unlimited number of historical file versions, a standard functionality of the CrashPlan PRO software. Such a revision history means that different versions of files are automatically saved so that old data is still available even though the original file is overwritten or deleted. In emergencies where the damage becomes visible only later, think of viruses and hacking, it is important to return to a previous situation.

    Because of CrashPlan PRO is only storing the differences between two versions, not the entire file each time, old versions hardly take up any space. Deleted files can quickly fill up storage space, but nevertheless for safety purposes leave deleted files for at least 30 days in the backup copy.

    Backup versus archive

    In practice, backup and archive are often confused. Old versions within a backup are not archival storage. An archive is storing documents whose purpose is to keep this long-term. Often there is an archive for the business interest and/or legislation. The archive is an autonomous collection, the backup is the reserve copy.

    Problems in old versions and deleted files are never repairable because the original file on your computer is missing for verification.

    1 year after the original file is not present on your computer, the probability of failure estimated at around 33% in a pessimistic and 7% in an average scenario.
    Backups¹ Pessimistic (estimate)   Average (estimate)
      Failure probability after 1 year 1 on ... files   Failure probability after 1 year 1 on... files
    1 33%
    2 11%
    3 3,6%
    3 thousand
    4 1,2%
    42 thousand
    5 0,4%
    595 thousand

    ¹ number of available backup copies after a disaster

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  • Is secure

    CrashPlan PRO always encrypts all data on your system and sends it over an encrypted connection to Pro Backup wherever they are stored encrypted too. Here the names of the originals are not readable.

    Example of a backup stored on one of our servers
    How CrashPlan PROe names its backup folders and files, and part of a backup file its contents is shown.

    Storage is located within the European Union, in accordance with Dutch and European regulations.

    On request Pro Backup staff can assist you in disaster recovery, if you do not appreciate this, there are additional security/privacy options available.

    Security levels within the CrashPlan PRO software
    Level Strength Passwords Process in case of loss Key distribution Backup access:
    customer +
    1. Default
    *** 1 Password recovery Automatic Pro Backup
    2. Data password
    **** 2 Order new account Automatic -
    3. Private key
    ***** 1 + 76 characters Order new account Manual -
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  • Restores easy and reliable

    CrashPlan PRO has support for different operating systems. It runs equally well on Windows, Macintosh, Linux and Solaris. By CrashPlan PRO software or via the secure web page, you can restore your files from any computer – even if it is a different operating system.

    To ensure that files are properly secured data validation is important. CrashPlan PRO does this by applying MD5-hashfunctions on the file content. Even a small change will result in a different MD5 checksum. With 820 billion files there is a 0,000000000001734% chance that two different files will lead to the same checksum result. With less files, this chance is even smaller. Furthermore the wserver periodically the integrity of the backups.

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For best data protection we always recommend backing up your devices to at least two destinations.

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