Note - This article is based on v2.6 and above (or v22.214.171.124 beta), while the basic balancing methods are supported in earlier versions, the advanced features described, and to some extent, overall balancing performance, is much improved in v2.6
Drive Bender can use a number of different methods to balance files across drives in a pool. The primary reason a pool should be balanced is to ensure the pool can write a primary and duplicate file to the pool while maintaining the maximum space on each drive in the pool.
Balancing occurs at two events, 1) when writing a file to the pool for the first time, Drive Bender, based on the balancing method, determines the target drive... and 2) when background balancing is being performed, Drive Bender may move a file from one drive to another to best achieve the target balancing method (not all balance method support background balancing).
Even: Drive Bender attempts to keep the percentage used on all drives even across the pool.
- Pro - This provides the best free space ratio on multiple drives, which is best for pools that use duplication. Even load, both in terms of files and general usage across the pool.
- Con - This can be problematic on pools that utilize vastly different size drives. On pools with many large files, it can be difficult to balance effectively. When seeking a file, on average half the drives in the pool must spool up to find the file.
Cascade: Drive Bender fills each drive in the pool one after the other, using the volume label as a means of ordering the drives (aka DB1 to DBx). The order is determined by the date in which the drives are added (you can tweak this, see - Can I alter the cascade order of the drives in a pool).
- Pro - Fast and easy to maintain. For pools with low utilization (aka lots of free space), access performance is improved because the average file position will be closer to the first drive.
- Con - Not great for duplication with the chance of a drive running low on space and causing a write abort error. Not all space on a drive can be used, Drive Bender will flag a drive as full even with space left (this needs to happen to prevent running out of space).
Most space: Drive Bender simply picks the drive with the most space. Note this method is not supported for background balancing.
- Pro - Light on system resources as no background balancing is performed.
- Con - No good for systems running duplication as background balancing is not performed.
With the balancing improvements that were made in v2.6, we also enabled a folder level balancing mode that was in developed for v2, but never made it to the final v2 release. It is important to note this mode is limited and not supported by the Drive Bender Manager, it requires registry manipulation and changes to individual drives in the pool (also note that accessing any balancing option from the Manager may overwrite any manual setting made). There are three additional modes
Folder: Drive Bender will write all files to the target folder/drive, however, if none specified, will revert to "most space" method.
Folder / Even: Drive Bender will write all files to the target folder/drive, however, if none specified, will revert to "even" method.
Folder / Cascade: Drive Bender will write all files to the target folder/drive, however, if none specified, will revert to "cascade" method.
It should be noted that using Folder method, reverting to "most space" is only applicable for the initial file write, and not background balancing.
Setting up in the registry
Open regedit and head to "HKEY_LOCAL_MACHINE\SOFTWARE\Division-M\Drive Bender", here you will find an entry call "Balancing Method" (DWORD value). Set as follows (decimal) - Folder: 1, FolderEven: 4, FolderCascade: 5
To specify a target folder, you need to open a target drive in the pool (to map a drive letter to a target drive, click here), then find the target folder and add an empty file called "FOLDER.TARGET.$DRIVEBENDER".
Finally, this folder level balancing mode is experimental, we have no plans to add GUI support at this point in time. In addition, technical support for this feature will be limited.