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Backup, Replication Over Slow Connections (e.g. VPN, LAN, Network) with No Rescan

*** Requires ViceVersa PRO 2.5 build 2504 or any later version ***

When backing up files or replicating files over slow connections (such a VPN tunnel or a LAN), a major bottleneck is the re-scanning of the files over the slow side that needs to be done each time the profile runs.

The backup / replication is usually setup between a fast source (the local disk) and a slow target (the folder reachable over the network, VPN, LAN) or from a slow source to a fast target. If the number of files to scan is significant, the ViceVersa profile may spend most of its time performing the scanning of the slow side, rather than copying files. This may be impractical.

To work-around this issue, and to speed up the file comparison/scanning phase, we introduced a new feature in ViceVersa PRO 2.5 build 2504. The new feature is called “no rescan”.

When this feature is activated, source or target folders (the slow folders) are only scanned the first time the profile runs or if a certain custom condition is true.

After the first run, ViceVersa assumes that the files in the slow folders have not changed since the last execution and their content is loaded from the tracking database instead.

This significantly speeds-up the comparison and the overall backup process.

How to use the new “No Rescan” options:

The No Rescan options are located in profile settings -> performance / bandwidth. The following options are available:

Do Not Rescan (Source or Target): This option instructs ViceVersa not to rescan the source or the target folders each time. If the source is the slow side (e.g. VPN, LAN, Network folder), set this option to Source. If the target is the slow side, set this option to Target.
When this option is activated, selected folders are only scanned the first time the profile is run or if the rescan condition is true. After the first run, ViceVersa assumes that the files in the folders selected not to be rescanned have not changed since the last execution and their content is loaded from the tracking database instead. Therefore this option requires the tracking database to be enabled (ViceVersa will set one up automatically).

Rescan every X hours : Instructs ViceVersa to perform a full rescan and refresh the file list stored in the tracking database for the slow side every X hours (enter 0 to ignore). Use this option to rescan the slow folders occasionally to make sure no changes have occurred to them, outside ViceVersa, since the last scan.

Rescan if the following condition is true (Rescan Condition): Instructs ViceVersa to perform a new full rescan if the specified condition is true (leave condition blank to ignore). Operators =, <> (not equal), OR, AND, > (greater than), < (smaller than), >= (greater than or equal), <= (smaller than or equal) are supported.

The following variables can be used in the rescan condition:
  

Rescan Condition Variable

Explanation

Rescan Condition Examples

dayofweek

Day of the week (1 = Sunday, 2 = Monday, to 7 = Saturday)

dayofweek = 1 (performs a rescan on Sundays).
dayofweek = 1 OR dayofweek = 7
(performs a rescan on Sundays and Saturdays).
dayofweek <> 2
(performs a rescan if day of week is not Monday).

day

The day of the month, in the range 1 through 31

day = 15 OR dayofweek = 1 (performs a rescan on Sundays and on the 15 of every month).

hour

The current hour, in the range 0 through 23

hour >= 0 AND hour <= 7 (performs a rescan between midnight and 7:59 am).

minute

The current minute, in the range 0 through 59

minute > 30 (performs a rescan in the second half of each hour).

month

The month of the year, in the range 1 through 12 (1 = January, 12 = December)

month = 1 (performs a rescan in January).

year

The year, 1970 to 2038

year <> 2012 (performs a rescan if the current year is not 2012).

elapsed_days

The number of days that have passed since the last rescan

elapsed_days > 7 (performs a rescan if the number of days that have passed since the last rescan is greater than 7. Equivalent to every 7 days).

elapsed_hours

The number of hours that have passed since the last rescan

elapsed_hours > 4 (performs a rescan if the number of hours that have passed since the last rescan is greater than 4. Equivalent to every 4 hours).

elapsed_minutes

The number of minutes that have passed since the last rescan

elapsed_minutes > 30 (performs a rescan if the number of minutes that have passed since the last rescan is greater than 30. Equivalent to every 30 minutes).

By using the rescan condition, a rescan can be setup to happen periodically and automatically, for example weekly or overnight.

Other ways to force a rescan:

Beside instructing ViceVersa to perform a full rescan automatically every X hours or when a certain condition is true, a full rescan can also be "forced" in the following manner:

- Manually from the ViceVersa main window, by selecting "Compare with Rescan" or "Compare and Execute with Rescan" (see screen-shot below). Note that these two additional commands are only shown when the option "Do not rescan" is activated in the profile settings.

- From the command line using the /rescan flag.

- Manually from VVEngine, by clicking on "Run with Rescan" (requires VVEngine 2.0 build 2.003 or  newer). This additional command is only shown in VVEngine when the option "Do not rescan" is activated in the ViceVersa profile settings.



User Comments
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Julian -  29-Aug-11
Can I assume we shouldn't use the "no rescan" option if we wish to have two-way synchronization?
TGRMN Software -  30-Aug-11
Yes, that is correct, the synchronization method requires rescanning of both source and target. 'No Rescan' is for backup or replication (one-way copying). thanks
LSC -  22-Jun-16
So for a one-way sync, you don't need to turn on no-rescan on the target since that wouldn't change?
TGRMN Software -  22-Jun-16
Opposite, if you are doing a one-way replication and you know target does not change outside ViceVersa, do enable no-rescan for target to speed-up source/target comparison.
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