You bought a 1TB hard drive, plugged it in and Windows reported back 931GB. A 10TB surveillance setup ran out of room in six weeks.

An SSD that was supposed to last a decade started throwing warnings after three years. None of this is random it all comes down to math and once you understand it, you stop getting caught off guard.

1. Why Windows Reports Less Space Than the Label Says

Every hard drive you have ever bought was technically telling the truth. The problem is that manufacturers and operating systems count bytes using different methods and the gap between them grows as drives get larger.

Drive makers calculate capacity using base 10. In their world, one kilobyte equals exactly 1,000 bytes, one megabyte is 1,000,000 bytes and one terabyte is exactly one trillion bytes. Clean and simple.

Windows works in base 2. One kilobyte on your PC is 1,024 bytes not 1,000. That small difference compounds at every level.

Windows Math: 1 TB = 1,099,511,627,776 bytes

Manufacturer Math: 1 TB = 1,000,000,000,000 bytes

When Windows reads a 1TB drive, it takes those one trillion bytes and divides by 1,024 three consecutive times to reach gigabytes. The result is 931GB. The larger the drive, the bigger the shortfall a 20TB drive loses close to 1.4TB purely from this unit difference.

2. RAID Configurations: What They Are and When to Use Them

RAID lets you combine multiple physical drives into one system. Depending on the configuration, that combination can prioritize speed, protect against failure or do both at a cost. Here are the setups you will actually encounter:

RAID 0 splits incoming data across two or more drives simultaneously. Read and write speeds are excellent, but there is no redundancy at all. A single failed drive wipes out everything in the array.

RAID 1 keeps an exact duplicate of every drive in the array. Lose one drive and your data survives untouched. The trade-off is that half your total storage goes toward maintaining that copy.

RAID 5 needs at least three drives and distributes both data and parity information across all of them. One drive can fail and the array stays intact, with the parity data used to reconstruct what was lost. This level is common in home and small business NAS setups.

RAID 6 builds on RAID 5 by adding a second layer of parity allowing the array to absorb two simultaneous drive failures. In larger arrays eight drives or more this matters because replacing one failed drive can take long enough that a second failure becomes a realistic risk.

RAID 10 combines mirroring and striping. Drives are paired as mirrors first then striped together.

It delivers the strongest combination of performance and protection but the entry cost of four drives minimum and only 50% usable capacity makes it a choice for environments where both speed and uptime are non-negotiable.

RAID Level — Minimum Drives — Usable Capacity — Drives That Can Fail RAID 0 — 2 — 100% — 0 RAID 1 — 2 — 50% — 1 RAID 5 — 3 — (N−1) drives — 1 RAID 10 — 4 — 50% — Up to 50%

3. How Much Storage Does a Surveillance System Actually Need?

Cameras running around the clock eat through storage faster than almost any other use case. Estimating accurately means accounting for four variables rather than guessing at a round number.

Resolution and bitrate go hand in hand. A camera shooting in 4K at 8 megapixels can demand 8 to 16 Mbps to record cleanly.

A 1080p camera typically needs only 2 to 4 Mbps. Put four 4K cameras where you had four 1080p cameras and your storage consumption can quadruple.

Compression codec choice has an outsized effect on the result. H.265, also called HEVC, encodes video roughly twice as efficiently as H.264 without any visible drop in quality. Switching your NVR or DVR to H.265 is the single fastest way to extend how long your existing drives last.

Frame rate shapes both footage quality and file size. Cinema typically runs at 24 FPS. For surveillance purposes, 15 FPS gives you smooth enough motion to identify people and events while meaningfully reducing daily data output compared to 30 FPS.

4. How Long Will an SSD Last? Understanding TBW

Solid-state drives do not wear out the same way spinning hard drives do. Flash memory cells degrade each time data is written to them and manufacturers quantify this limit using a rating called TBW — Terabytes Written.

A quality 1TB NVMe drive might carry a 600 TBW rating. What that number means in practice depends entirely on your write habits.

A typical home user writing around 50GB per day would take approximately 12,000 days — just over 32 years to reach that limit. A video editor pushing 500GB of writes daily would reach the same threshold in roughly three years.

One habit that extends SSD lifespan noticeably: keep between 10% and 20% of the drive free at all times.

The drive's controller uses that empty space to spread writes evenly across all flash cells through a process called wear leveling. When the drive is packed to capacity, some cells get hit repeatedly while others sit idle, and that imbalance accelerates wear.

5. Why Your SSD's Advertised Speed Is Not What You Get in Real Life

A drive rated for 1,000 MB/s that transfers files at 400 MB/s is not broken it is being limited by something else in the chain. Transfer speed can never exceed the slowest component involved.

USB 2.0 tops out at around 60 MB/s regardless of the drive attached to it.

SATA III has a ceiling of roughly 600 MB/s, which is why even fast SSDs hit a wall when used with older connections.

NVMe Gen 4 removes that ceiling almost entirely, with peak speeds reaching 7,500 MB/s on current hardware.

File count matters as much as file size. Moving a single 50GB video file is fast. Moving 10,000 small photos that total 50GB takes much longer because the operating system opens, processes, and closes each file individually. The overhead adds up fast.

6. Real Storage Needs for Media and Gaming in 2026

To put actual drive capacity in context here is what a true 931GB of usable space on a "1TB" drive realistically holds:

AAA games now average between 80GB and 120GB each meaning a 1TB drive fits roughly 8 to 12 titles before you are uninstalling to make room.

4K UHD movie files at high bitrate land between 40GB and 50GB, giving you around 18 to 22 films per terabyte.

Standard smartphone photos at roughly 4MB per JPEG average out to around 230,000 images per terabyte.

MP3 music files at a typical 5MB each fit approximately 180,000 songs per terabyte.

For general office use, 512GB covers day to day needs comfortably. Gamers treating 2TB as the baseline avoid the constant rotation of installs and deletions.

Anyone running RAID arrays or multi-camera surveillance setups should calculate their actual requirement first then add 20% on top to account for system overhead, metadata and unexpected growth.

The math behind storage is not complicated once you know what drives it. Apply these numbers to your setup and you will size your storage correctly the first time rather than discovering the problem after the fact.