Snapshots of any Linux Block Device
The R1Soft Hot Copy utility creates an instant point-in-time volume snapshot of any block device while the system is running without interrupting applications.

Consistent Point-in-Time Linux Volume Snapshots
Hot Copy very quickly and efficiently puts even the busiest file systems into a totally consistent state for brief instant to take a point-in-time snapshot.

Copy-on-Write Volume Snapshot Method
As block level changes are made to the real device (e.g. your hard disk) hot copy makes a backup copy of the changed block.  The changed blocks are efficiently stored in unused space on your hard disk.  These stored changed blocks maintain a point-in-time snapshot and space is only needed when you make changes to the real device.

High-Performance Volume Snapshots (Outperforms LVM Snapshots)
R1Soft is constantly working to improve its Linux Volume Snapshot technology.  Hot Copy 3.3.0+ has built-in file system awareness for Ext2/3 (Ext4 coming soon) and ReiserFS 3.  File system awareness means it knows what parts of the block device are used by the file system. 

When you write to unused blocks on the disk Hot Copy is smart enough to Not perform a copy-on-write for these disk writes.  This means it typically outperforms LVM Snapshots.

Hot Copies are Readable AND Writable
You can even write to your snapshots if you want.  This utility open up seemingly endless possibilities for usefulness in system administration.

Requires No Dedicated Volume Snapshot Device or Storage
Automatically Hot Copy uses free space on your block device (e.g. hard disk) to store changed blocks.  This means you can use hot copy on any device that has some free space.  Unlike LVM you don’t need dedicated Volume Group space to maintain the snapshot.  Optionally you can specify an alternate device with more space for hot copy to use as a changed block store.  The device hot copy uses to store changed blocks can even be mounted as it uses space without interrupting the file system.

Create Multiple Volume Snapshots
With Hot Copy 3.3.0 you can create multiple point-in-time snapshots for the same block device.