Preallocation of Storage

What is the principal argument against pre-allocating (formatting) the storage for the video database?

One problem that I am aware of is if you need to pre-allocate space for each camera. A camera with very little motion might record for 100 days in a 100 GB allocation, while a busy one might have just 1 day. Change the parameters and it gets real hard to figure out what a reasonable size should be.

But say that you pre-format the total storage you need for the entire system, and then let all the cameras share the storage on a FIFO basis. This way, all cameras would have roughly the same amount of time recorded in the database.

My, decidedly unscientific tests, show that writing a large block of data to a continuous area on the disk is much faster than writing to a file that is scattered across the platters. Disk drives now have large caches and command queuing, but these mechanisms were designed for desktop use, and not a torrent of video data being written and deleted over and over again.

Some people balk at the idea that you pre-format the disk for reasons I simply do not understand. If you have a 100 TB storage system, I would expect that you’d want to use the full capacity of the disk. There are no points awarded for having 20% of the disk empty, so why do people feel that pre-allocation is bad?

Any takers?

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