Highly Reliable Systems: Removable Disk Backup & Recovery


High-Sync: Block Level Backup – Block Level Copying

By Nicholas Bailey

Using High-Sync for Block-level Backup and Block-level Copying.

High-Sync can detect which parts of a larger file have changed, and copy only the changed blocks, rather than the complete file. Copying only the changed blocks can save bandwidth, and time, especially over a slow connection. When copying between local disks, or in a LAN environment, can save bandwidth too, but may not always save much copying time, because the source file has to be read in its entirety every time in order to determine the changed blocks.

Only block-oriented file types are eligible for block-level copying. These include database files, such as SQL, or Outlook PST, as well as drive images, and virtual hard disk images (VMs). Alternatively, stream-based files will usually cause all blocks to be changed whenever they are modified. Thus, block-level copying will not be able to save much bandwidth with stream-based files.

In High-Sync, block-level copying is called ‘Partial File Updating.’ In many cases, you need to choose only this one, via a check-mark, which is on the ‘Special’ settings category, in ‘Advanced Mode.’

The program needs to have fast access to at least one of the sides of the synchronization. The other side may be a low-bandwidth connection. If you are using an ‘Internet Protocol,’ please note that only SSH/SFTP supports block-level updating directly. The other protocols can only be used with ‘Synthetic Backup.’

Note: Block level copying with SSH/SFTP has only been implemented for uploads, not downloads.


Partial File Updating can work in three varying ways:

1: With Database:
– Source access must be fast.
– Destination may be slow.
– MD5 check-sums are stored in the database.
– Destination files must not be modified by any other profile, person, or tool.
– Destination must be accessed via LAN, VPN, or SSH/SFTP.

2: With Remote Service:
– High-Sync Remote Service computes MD5 check-sums on remote computer.
– The ‘slow’ side can be both the source, or the destination.
– MD5 check-sums are newly calculated each time.
– Files on both sides can be modified by other profiles, persons, or tools.
– One side must be local, or LAN/VPN, the other can be LAN, VPN, or SSH/SFTP.

3: Synthetic Backup:
– Similar to Mode 1, but adds ‘Zip’ compression, versioning, and filename encoding.
– Can work locally, or with any ‘Internet Protocol,’ for the destination side.
– The changed blocks are uploaded in a new, separate zip file every time.
– All older zip files must stay on the backup storage, but can be thinned out.
– All connection types and ‘Internet Protocols’ are supported.


1: Slow Destination
In this mode, the speed-up is available when you copy files from a location to which you have fast access (preferably your own hard disk). The destination can be a slow connection, but it must be a normal file system (either LAN or VPN), or SSH/SFTP. For other connections, you can use the Synthetic Backup.

Using Number 1:
In your profile, make the following check-mark: ‘Use Partial File Updating,’ which is on the ‘Special’ tab sheet when editing the profile in ‘Advanced Mode.’ The next time you run the profile, a database is created on your hard drive where information needed for the speed-up is stored. The second time you run the profile, you should notice the speed-up.


2: With Remote Service
This mode can speed up updating large files in both directions. The remote computer can be both source and/or destination. This is achieved by running a small service application on the remote computer, which will create the necessary check-sums on the fly, when requested by the main application running on a different machine.

The other (local) computer, where the main High-Sync program is running, needs to have normal file system access to the remote computer (LAN or VPN), or it can use SSH. It needs to have write access to the remote computer, in order to save the checksum request file there. The MD5 check-sums are created when needed, so that no database is being used.

Using Number 2:
On the remote system, run the ‘Setup’ program and install the High-Sync ‘Remote Service,’ along with its control panel. Start the control panel from the High-Sync group in the ‘Start’ menu. On the tab sheet, ‘Configure Check-summer,’ and enter the base folders that will be used for synchronization. Click ‘Apply.’ On the tab sheet ‘Service Configuration,’ click on ‘Install Service and ‘Start.’ The service will be using the ‘Windows System’ account by default. If this account does not have sufficient access privileges, you may have to change the account in ‘Windows Control Panel’ > ‘Administrative Tools’ > ‘Services.’

On the local system, you are running the main High-Sync program. In your profile, the right-hand side must be the remote system. Specify one of the folders which you have specified for the remote service to monitor. The left side should be your local folders, or a network drive, with relatively fast access. On the ‘Specials’ tab sheet in’ Advanced Mode,’ make the following check-marks: Use ‘Partial File Updating’ and ‘Right side uses Remote Service.’


3: Synthetic Backup
This feature is intended for backing up from a local storage to any type of backup storage. The backup can be local, or online.

Choose ‘Synthetic Backup’ on the tab sheet ‘Versioning>Synthetic Backup.’ This will automatically place these additional check-marks:
– Use Partial File Updating (under Special).
– Filename Encoding (under Versioning).
– Zip Each File Individually (under Zip/Encryption).

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