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UBC Mathematics: MathNet FAQ [File Recovery]

UBC Mathematics: MathNet FAQ [File Recovery]

Question: I have deleted/overwritten my file. Can I recover the lost data?
Author: Joseph Tam
Date: Dec. 12, 2010

Maybe. It depends on where and when you lost the data.

Location of data to be recovered

MathNet centralized file storage

Our centralized file storage contains the following data

Data Original Data Location Snapshot Location
Home directory Unix: /nfs/user
Windows: \\samba\user
Unix: /nfs/snap.home/snapname/user
Windows: \\samba\home_snapname
Web directory Unix: /nfs/HomeWeb/user
Windows: \\samba\HomeWeb
Unix: /nfs/snap.web/snapname/user
Windows: \\samba\web_snapname
Mail INBOX Unix: /nfs/mail/user
Windows: N/A
Unix: /nfs/snap.mail/snapname/user
Windows: N/A
Mail Folders Unix: /nfs/user/mail
Windows: \\samba\user\mail
Unix: /nfs/snap.home/snapname/user/mail
Windows: \\samba\home_snapname\mail
Windows Common Folder Unix: /nfs/user/.windesk
Windows: \\samba\user\.windesk
Unix: /nfs/snap.home/snapname/user/.windesk
Windows: \\samba\home_snapname\mail\.windesk
Personal workstation backup Unix: /nfs/backup/user
Windows: N/A
Unix: /nfs/snap.user/snapname/user
Windows: N/A

Some owners of personal workstations have pre-arranged nightly backups. Backups takes place every 24 hours at a designated time, and therefore, hourly snapshots do not change unless they straddle the designated backup time.

snapname refers to the particular snapshot (i.e. when the snapshot was taken). It is explained in the section Retrieval from Snapshots below.

user refers to your username.

The data contained in this storage is backup'd (snapshot) every hour at the top of the hour, and 10 hours' worth are kept. Additionally, nightly snapshots are taken every midnight and kept for 7 days. A weekly snapshot is also taken at Sunday midnight, and last 4 are kept. Thus, it is possible to retrieve data for up to 5 weeks.

Snapshots cannot be kept indefinitely, so it is important to retrieve lost data as soon as you are able to, otherwise it may be purged before you can get to them.

Retrieval from Snapshots

  • Step 1: Understanding snapshot names

    Snapshot archives are available from our public Unix workstations. A subset of all available archives is also available from our public Windows workstations (e.g. ladybug, beetle). They contain exact replicas of the data at the time the snapshot was taken.

    Each snapshot archive have names that reflect the age of the snapshot.

    Snapshot names
    hourly.0, ..., hourly.9
    These directories contain hourly snapshots taken at the top of the hour with hourly.0 being the most recent and hourly.9 being the oldest snapshot.
    nightly.0, ..., nightly.6
    The nightly snapshots are taken at midnight daily, with nightly.0 being the most recent and nightly.6 being the oldest snapshot.
    weekly.0, ..., weekly.3
    Weekly snapshots are taken at the start of Sunday at midnight; weekly.0 was taken at the most recent Sunday, and weekly.1 the Sunday previous to that, etc.
    Windows (UNC or Icon name)
    hour or Last hour
    Same as "hourly.0" explained above.
    night or Last night
    Same as "nightly.0" explained above.
    week or Last Sunday
    Same as "weekly.0" explained above.

    No two snapshots are taken at the same time; if two snapshots coincide (e.g. at Sunday midnight, the hourly, nightly, and weeky snapshots coincide), the longer interval snapshot takes precedence and the rest skipped. So for example, at Tuesday 02h15, the list of snapshots in increasing age is

    hourly.0 (taken at Tuesday 02h00)
    hourly.1 (taken at Tuesday 01h00)
    nightly.0 (taken at Tuesday 00h00)
    hourly.2 (taken at Monday 23h00)
  • Step 2: Finding which snapshot has your data

    It would be wise to recover data as soon as you realize it is gone. You have 4-5 weeks to recover your data before the oldest snapshots disappear. Furthermore, if the file is modified often, the hourly changes are only kept for 10 hours, then disappear, leaving only the nightly version available.

    In general, you should start searching for the data from the newest to the oldest snapshots. If you cannot remember the name of your lost data or when you lost it, you have a long search ahead of you.

    • (Unix)

      If you know the file or directory name of what you want to recover, for example,

      you can use "ls" to look for that file sorted by modification time:
      	ls -lt /nfs/snap.home/*/schmuk/Recipes/Goulash/spicy.txt
      If this does not tell you which version you want, then you'll have to examine the contents of each snapshot version.

    • (Windows)

      Navigate the snapshot folders until you find the data you want to recover.

  • Step 3: Recovering your data
    • (Unix)

      Once you have found your lost data, you must copy it out of the snapshot archives back into your home directory or wherever it should go. The snapshot archives are immutable, so you cannot delete, rename, or modify them.

      	cp /nfs/snap.home/hourly.0/schmuk/Recipes/Goulash/spicy.txt recover.txt
      If you've need to transfer a lot of files (e.g. a whole directory with zillions of files and subdirectories), you can use this method to copy an entire directory and its subdirectories:
      	cd /nfs/snap.home/hourly.0/schmuk/
      	tar cf - Recipes | (cd /some/safe/dir; tar xvf -)
    • (Windows)

      Copy the snapshot file/folder back onto your desktop or filespace (i.e. usual drag and drop operation).

    Public workstation's local storage

    Examples of data stored on public workstation's local storage are

    • Temporary directories such as
      Unix: /tmp, /var/tmp
      Windows: C:\TEMP
    • Data held on personal workstations and laptops that do not have pre-arranged nightly backups.
    • Windows: Files/folders on desktop, application folders.

    This data is not backed up. You can see the section Other Places to Look to help you recover lost data.

    Other Places to Look

    • Trash: some desktops (e.g. Windows, GNOME) will not remove files immediately, but place them in a temporary location represented by a trash can icon. It may still be there.
    • Application backups: some applications will make copies of data before modification. Look for filenames suffixed with '~', '.bak', '.old', '.sav', '.orig', '#', etc.
    • Email: if you have sent (or received) the data in the form of an Email attachment, it may still be in one of your mailboxes.
    • Recovery software: for personal workstation, file recovery software may be avilable that reovers deleted files. If the data is important, do not use the computer: use of the storage device may permanenlty overwrite your old data.
    • Copies: if you have received/sent copies from/to other people, they may be able to replace your copy.