Last post was very clear on discussing the snapshot size as there was no follow up question from the response. This part is what is important about snapshot sizing that I will copy and past again. “Please set as snapshot size as much space as you expect to change during active snapshot. E.g. when you are doing backup from snapshot which takes one hour please set this snapshot size to as much space that will be changed during one hour.” Concerning the inserting of the manual, a lot of new customers do not have time to download the manual and this saves them time as you can see there was no reply so he understands.

Snapshot is based on the point in time difference (or known as Delta after the change) of the Logical Volume “The storage of all changes is independent of the file-system - it takes place on block-level” .

In your case if you have 300GB LV and you feel there will be changes during the time that you have specified that will exceed a certain amount lets say 30GB +or- during this time then you would set 10% -15% snapshot of the designated 300GB volume. Snapshots
Will not overwrite another snapshot only update after re-activating it again in the Maintenance > Snapshot function then it will update from dataset changes of the Logical Volume. Please read the manual and create test so you can see how this process works also remember to limit your snapshots as this will effect performence.

I also have some additional information on our Snapshot technology as it is based on
Copy-on-write (sometimes referred to as "COW") this is an optimization strategy used in computer programming. The fundamental idea is that if multiple callers ask for resources which are initially indistinguishable, you can give them pointers to the same resource. This fiction can be maintained until a caller tries to modify its "copy" of the resource, at which point a true private copy is created to prevent the changes becoming visible to everyone else. All of this happens transparently to the callers. The primary advantage is that if a caller never makes any modifications, no private copy need ever be created.
Copy-on-write finds its main use in virtual memory operating systems; when a process creates a copy of itself, the pages in memory that might be modified by either the process or its copy are marked copy-on-write. When one process modifies the memory, the operating system's kernel intercepts the operation and copies the memory so that changes in one process's memory are not visible to the other.
Another use is in the call function. This can be implemented by having a page of physical memory filled with zeroes. When the memory is allocated, the pages returned all refer to the page of zeroes and are all marked as copy-on-write. This way, the amount of physical memory allocated for the process does not increase until data is written. This is typically only done for larger allocations.
Copy-on-write can be implemented by telling the MMU that certain pages in the process's address space are read-only. When data is written to these pages, the MMU raises an exception which is handled by the kernel, which allocates new space in physical memory and makes the page being written to correspond to that new location in physical memory.
One major advantage of COW is the ability to use memory sparsely. Because the usage of physical memory only increases as data is stored in it, very efficient hash tables can be implemented which only use little more physical memory than is necessary to store the objects they contain.
The COW concept is also used in virtualization/emulation software such as Bochs, QEMU, and UML for virtual disk storage. This allows a great reduction in required disk space when multiple VMs can be based on the same hard disk image, as well as increased performance as disk reads can be cached in RAM and subsequent reads served to other VMs out of the cache