IO Industries Inc.

Why does deleting recordings not always free up space?

The DVR Express Core file system does not support recording to multiple blocks of free space. De-fragmentation of the file system is not supported as it is time consuming and risks loss of data. The scratch file created prior to recording always uses the largest continuous block of free space on the drive set.

For example, suppose five recording of varying length are created on a drive set that was initially empty (see figure below). Observe the largest continuous block of available space is at the end of the drive set. A sixth recording could be created that uses the remaining 20%.
 


Now suppose the files #2 and #4 are deleted (see figure below). Observe the total amount of free space increases to 60%, however the maximum new file size is limited to 30% because the largest continuous block of free space is only 30%.


To use the remaining 60%, files #3 and #5 would need to be exported (if necessary) and deleted.
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