Re: backup the entire server

From: Aleksandar Milivojevic (amilivojevic_at_pbl.ca)
Date: 04/14/05

  • Next message: Rick Stevens: "Re: SCSI disk errors, but disk diagnostics say disk is OK" 
    Date: Thu, 14 Apr 2005 12:58:03 -0500
To: For users of Fedora Core releases <fedora-list@redhat.com>

    Claude Jones wrote:

    > Contrary to the subject line, BackupPC doesn't NOT back up the entire server,
    > at least in WindowsLand. All files that are locked, which include things like
    > your Outlook .pst file, and many operating system files, will NOT be backed
    > up. I am too new to Linux to know how this issue plays out in the Linux
    > world.

    I Unix world, there are no mandatory file locks, only advisory locks.
    If application chooses to ignore the lock, nothing is preventing it from
    accessing the file (including removing the file that some other process
    keeps open).

    So, backup application under Unix *can* backup the locked file, if it
    chooses to ignore the locks (or doesn't check for them). However, if
    the file was being kept open by some other application for writing, the
    content of the file might be corrupted/unusable after restore is
    performed (not to be confused with corrupted buckup or file, the backup
    and file will be OK, only the content might get corrupted).

    There are couple of solutions to the problem:

      - stop applications that keep file open, then do the backup

      - simlar to above, if under LVM, make snapshot (instant operation),
    restart applications, do backup of snapshot, delete snapshot

      - similar to previous (but redundancy lost while backup runs), if on
    software RAID1, flush dirty pages to disk, detach one submirror, do the
    backup, than reattach the mirror (Solaris has a nice feature that Linux
    lacks, Solaris allows submirror to be offlined, instead of detached, in
    which case no resync of entire mirror is needed, only changed blocks are
    synced, plus handy lockfs command that prevents new dirty pages to be
    created between sync and offline (or detach) operations, so you are
    guaranteed to have correct data on offlined (or detached) submirror).

      - use application's backup module to do safe backups. most databases
    come with some kind of dump tool, some come with its own backup tools
    and/or modules for backup systems such as Legato Networker or Veritas
    Netbackup), and some can create snapshots. safe to use on live database
    as long as database supports transactions and/or locking *and*
    applications that access database are using them correctly (in other
    words, they don't leave database in unconsistent state between two
    transactions or wile tables are unlocked). if your database can't be
    brought down not even for milisecond, this might be the only option for
    making a backup of it. 

    -- 
Aleksandar Milivojevic <amilivojevic@pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7
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  • Next message: Rick Stevens: "Re: SCSI disk errors, but disk diagnostics say disk is OK"

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