Dynamic allocation

By default, a RAM disk allocates its full size in memory as soon as it is mounted. For example, a 4 GB RAM disk will immediately consume 4 GB of RAM regardless of how much data is actually stored on it.

With dynamic memory allocation enabled, the RAM disk allocates memory only as needed. The memory footprint grows as you write data to the disk and, when combined with TRIM support, shrinks when you delete files.

How it works

When dynamic allocation is enabled, the RAM disk driver divides the virtual disk space into regions. Instead of allocating all regions upfront, it allocates them on demand when data is written to previously unused areas. This means:

• A newly created RAM disk with dynamic allocation might only use a few megabytes of RAM initially (for file system metadata).
• As you copy files to the disk, memory usage grows proportionally.
• The maximum memory usage is still limited to the configured disk size.

Automatic memory release (TRIM)

Modern file systems support the TRIM command, which informs the storage device when data blocks are no longer in use. When you enable Automatically release memory (TRIM), the RAM disk driver responds to these TRIM commands by freeing the associated memory regions.This means that when you delete files from the RAM disk, the memory they occupied is returned to the system. Without TRIM, deleted file space remains allocated even when it is no longer in use.

Memory reclamation is performed by a garbage collector running in the background. It may take a couple of minutes for the freed memory to become available to the system after files are deleted.

Note: TRIM support requires dynamic allocation to be enabled and is only available with the NTFS and exFAT file systems. Other file systems do not send TRIM commands, so memory cannot be automatically released.

NTFS vs exFAT for dynamic volumes

Both NTFS and exFAT support TRIM and work well with dynamic allocation. Here is a comparison to help you choose:

For most RAM disk use cases on Windows, NTFS is recommended due to its robustness and optional compression support. If you need minimal overhead, you can choose exFAT.

Advantages of dynamic allocation

• Efficient memory usage: Only the memory actually needed is allocated, leaving more RAM available for other applications.
• Memory reclamation: With TRIM enabled, deleting files returns memory to the system.
• Flexible sizing: You can create a larger RAM disk as a “maximum capacity” without immediately consuming all that memory.

Considerations

• Slight overhead: Dynamic allocation requires tracking which regions are allocated, adding small CPU and memory overhead.
• File system requirement: Automatic memory release only works with NTFS and exFAT. While NTFS natively supports TRIM, Windows does not implement TRIM for exFAT. Instead, RAM Disk driver parses the exFAT file system bitmap to detect deallocated clusters.
• Memory pressure: To maintain system stability, the driver will stop allocating memory when 1 GB or less of RAM remains available. If this occurs, I/O operations to the RAM disk will appear stalled until memory is freed. You can resolve this by closing other applications to free up memory, or by deleting files from the RAM disk. In the latter case, NTFS handles this scenario better than exFAT due to its more immediate TRIM processing.

How to choose dynamic or static allocation

Dynamic allocation is recommended when:

• You want efficient memory usage and do not need the full RAM disk capacity immediately.
• Your RAM disk usage varies significantly over time (files are frequently created and deleted).
• You want to create a larger capacity RAM disk without committing all the memory upfront.

Static allocation is recommended when:

• You need guaranteed memory reservation for critical applications.
• You prefer simpler, more predictable memory behaviour.
• You are using FAT or FAT32 file systems that do not support TRIM.