How Much Storage for 4 Security Cameras?

Quick answer

For four cameras recording continuously at an average 4 Mbps per camera, plan for approximately:

• 173 GB per day
• 1.21 TB for 7 days
• 3.63 TB for 21 days
• 5.18 TB for 30 days

Those figures are before allowing for filesystem overhead, surveillance metadata, RAID layout, and free space. Motion recording can use substantially less capacity, but the result depends on how often each camera detects activity and how the recording system handles pre- and post-event footage.

The most reliable way to size storage is to use the cameras’ actual average bitrate, recording schedule, and required retention—not camera count alone.

The inputs that determine storage

Use these five inputs when planning storage for four cameras:

1. Number of cameras
2. Average recording bitrate
3. Codec and resolution
4. Recording schedule
5. Retention period

Camera bitrate

Bitrate is usually the most useful input. It may be listed in Mbps (megabits per second) and can be:

• A fixed bitrate
• A maximum bitrate
• An average bitrate for variable-bitrate recording

For sizing, an average bitrate is preferable. If only a maximum bitrate is available, use it for a conservative estimate, then review actual storage consumption after deployment.

Resolution alone does not determine storage. A highly compressed camera with low scene movement may use less bandwidth than a higher-bitrate camera at the same resolution. Night scenes, foliage, rain, traffic, and other movement can increase the bitrate required by variable-bitrate encoding.

Codec

H.264 and H.265/HEVC can produce different storage requirements at comparable image quality, but the result depends on camera settings, scene complexity, frame rate, and the recorder’s support for the codec.

Do not assume that a codec automatically cuts storage by a fixed percentage. Use the bitrate reported by the camera or surveillance software whenever possible.

Recording schedule

There are two common approaches:

• Continuous recording: The camera records 24 hours a day.
• Motion or event recording: The camera records only when activity is detected, sometimes with a pre-event and post-event buffer.

Continuous recording is easier to predict and provides a more complete record. Motion recording reduces storage use, but activity levels can vary widely. A driveway, street, or busy entrance may record much more often than a quiet indoor room.

Retention

Retention is the number of days of footage you need to keep before older recordings are overwritten. Common requirements include:

• Several days for basic incident review
• Two to four weeks for many small businesses or homes
• Longer periods for regulated, contractual, or insurance-driven use

Retention should be defined per camera if different cameras have different importance or recording schedules.

The storage formula

For continuous recording, use:

Storage per day (GB) = Bitrate (Mbps) × 10.8

For multiple cameras:

Storage per day (GB) =
Number of cameras × Average bitrate (Mbps) × 10.8

For a retention period:

Retention storage (GB) =
Number of cameras × Average bitrate (Mbps) × 10.8 × Retention days

Then allow for system overhead and free space:

Planned usable capacity =
Retention storage × Overhead factor

An overhead factor of 1.10 to 1.20 is a practical planning allowance for filesystem overhead, recording indexes, metadata, and keeping some free space. The exact requirement depends on the NAS, filesystem, surveillance application, snapshots, and how much free capacity you want to maintain.

Why the 10.8 factor works

A megabit is one-eighth of a megabyte:

Bitrate (Mbps) / 8 = Megabytes per second

There are 86,400 seconds in a day:

Bitrate (Mbps) × 86,400 / 8 / 1,000
= Bitrate (Mbps) × 10.8 GB per day

This uses decimal gigabytes and terabytes. Operating systems and storage vendors may display capacity using different units, so small differences in reported capacity are normal.

Worked example: four cameras recording continuously

Assume:

• 4 cameras
• 4 Mbps average bitrate per camera
• 24/7 recording
• H.264 or H.265, with the bitrate already measured or selected
• No audio bitrate included in the estimate

Daily storage

4 cameras × 4 Mbps × 10.8
= 172.8 GB per day

Retention storage

Retention	Estimated footage
7 days	1.21 TB
14 days	2.42 TB
21 days	3.63 TB
30 days	5.18 TB

Adding a 15% planning allowance:

Retention	Footage plus 15% allowance
7 days	About 1.39 TB
14 days	About 2.78 TB
21 days	About 4.17 TB
30 days	About 5.96 TB

These are capacity estimates before accounting for RAID. If you need 30 days of continuous retention, a storage pool with roughly 6 TB of usable capacity would be a more realistic starting point than a pool advertised as exactly 5.18 TB.

Motion recording example

Suppose the same four cameras have a combined recording duty cycle of 25%. This means they record, on average, for one-quarter of the time. This is only an estimate; each camera may have a different activity level.

Continuous daily storage × Motion duty cycle
= 172.8 GB × 0.25
= 43.2 GB per day

For 30 days:

43.2 GB × 30
= 1,296 GB
= About 1.30 TB

With a 15% allowance:

1.30 TB × 1.15
= About 1.49 TB

Motion recording may require more than this simplified estimate because of:

• Pre-event recording
• Post-event recording
• Motion detection that triggers too often
• False positives from rain, shadows, insects, trees, or headlights
• Different activity levels between cameras
• Continuous low-resolution recording combined with higher-resolution event clips

For a new system, size for the likely motion duty cycle but retain enough capacity to handle busier periods. Review the recorder’s actual daily consumption after installation.

Compare different bitrates

The following table shows continuous storage for four cameras. These are formula-based examples, not claims about any particular camera model.

Average bitrate per camera	Four-camera storage per day	7 days	30 days
2 Mbps	86.4 GB	604.8 GB	2.59 TB
4 Mbps	172.8 GB	1.21 TB	5.18 TB
6 Mbps	259.2 GB	1.81 TB	7.78 TB
8 Mbps	345.6 GB	2.42 TB	10.37 TB

If your cameras use different bitrates, calculate each camera separately:

Total daily storage =
(Camera 1 bitrate × 10.8) +
(Camera 2 bitrate × 10.8) +
(Camera 3 bitrate × 10.8) +
(Camera 4 bitrate × 10.8)

This is more accurate than multiplying one camera’s estimate by four.

Network throughput and write workload

Storage capacity is only one part of surveillance sizing. The NAS or NVR must also receive and write the camera streams reliably.

Camera network bandwidth

For four cameras at 4 Mbps each:

4 cameras × 4 Mbps
= 16 Mbps total camera traffic

In megabytes per second:

16 Mbps / 8
= 2 MB/s theoretical payload

The actual network requirement is higher after accounting for protocol overhead, bursts, viewing streams, audio, and other NAS traffic. Camera streams may also use different bitrates for recording and live viewing.

Check:

• The cameras’ network connections
• The PoE switch budget and uplink
• The NAS or NVR network interface
• Whether live viewing, remote access, and backups share the same network
• Whether the surveillance application pulls streams through the switch or directly records them

Four cameras normally create a modest aggregate bitrate compared with many general-purpose NAS workloads, but reliability matters more than peak throughput. A camera stream that disconnects periodically can create gaps even when average bandwidth is low.

Storage write workload

Surveillance recording is generally a sustained write workload. Continuous recording is relatively predictable, while motion recording can create bursts when several cameras detect activity at once.

Choose drives and a storage layout intended for the expected workload. Consider:

• Drive workload ratings, if provided by the manufacturer
• The number of simultaneous camera streams
• Retention length
• Scrubs, rebuilds, snapshots, and other NAS tasks
• Whether the NAS will also serve files, run applications, or host media

Do not size only for the average write rate. Leave operational capacity for drive replacement, RAID rebuilds, backups, and other services.

RAID: useful for availability, not backup

RAID and ZFS storage pools can help keep surveillance recording available when a drive fails, depending on the selected layout. They do not replace a backup.

The usable capacity is less than the sum of the raw drive capacities:

• RAID 1: Approximately the capacity of one drive in a two-drive mirror
• RAID 5: Approximately the capacity of all but one drive, subject to implementation and overhead
• RAID 6: Approximately the capacity of all but two drives, subject to implementation and overhead
• RAID 10: Approximately half of raw capacity, with redundancy arranged as mirrored pairs
• ZFS RAIDZ: Usable capacity depends on the number and size of drives, RAIDZ level, filesystem overhead, and reserved free space

Use the NAS manufacturer’s or storage platform’s capacity calculator for an exact layout. Do not fill a pool to its theoretical maximum if the platform recommends preserving free space.

RAID trade-offs for surveillance

A mirrored or parity-based layout can preserve access after a drive failure, but it reduces usable capacity and may require a lengthy rebuild. During a rebuild, the system is under additional load and remains exposed to another failure depending on the layout.

For a small four-camera system, the practical choice depends on:

• Required retention
• Number of drive bays
• Tolerance for downtime
• Budget for replacement drives
• Whether footage is backed up elsewhere
• Whether the NAS also stores important files

If losing recorded footage is unacceptable, use both redundancy and a separate backup or export workflow.

NAS versus NVR

A NAS is a general-purpose storage server. It may support surveillance applications, file sharing, backups, media serving, containers, and other workloads.

An NVR is designed primarily to record, manage, and search camera footage. It may integrate cameras, motion detection, alerts, timelines, and camera-specific features more directly.

A NAS may be the better fit when you want:

• One system for surveillance and regular file storage
• Flexible storage pools and future applications
• Centralized backups
• A surveillance application compatible with your cameras
• Expansion into media or home-server workloads

An NVR may be preferable when you want:

• A focused surveillance appliance
• A simple camera setup and timeline interface
• Vendor-integrated camera management
• A system separate from household or business files

Before buying a NAS for surveillance, verify the software’s camera licensing model, supported camera protocols, codec support, recording limits, and hardware requirements. Compatibility can vary by NAS operating system and surveillance application. Do not assume that a camera’s ability to produce an RTSP or ONVIF stream guarantees every feature will work.

SSD cache: usually not the first upgrade

An SSD cache is not automatically useful for camera recording. Surveillance footage is usually written in a relatively steady stream, and cache benefits depend on the NAS software, access pattern, and what other workloads run on the system.

Before adding SSD cache, prioritize:

1. Sufficient usable capacity
2. Suitable hard drives
3. RAID or ZFS redundancy where appropriate
4. A reliable backup strategy
5. Adequate network and PoE infrastructure
6. Enough CPU and memory for the surveillance application

SSD cache may be worth investigating if the NAS also handles demanding file workloads, databases, virtual machines, or many simultaneous users. For a small four-camera system used mainly for recording, it is often not the most cost-effective first purchase.

ZFS considerations

ZFS can provide data integrity features, checksumming, snapshots, and flexible redundancy options, but it requires careful planning.

If using ZFS for surveillance:

• Choose a vdev layout that matches the required redundancy and expansion plan.
• Treat snapshots as additional storage consumers, not as backups.
• Maintain free space rather than planning to fill the pool completely.
• Use a separate backup or export destination for footage that must survive pool loss.
• Confirm that the surveillance application and NAS platform support the ZFS configuration you intend to use.

Expansion is especially important. Some ZFS layouts do not expand in the same way as a traditional hardware RAID array. You may need to add another vdev or replace drives according to the platform’s documented process. Plan future camera count and retention before buying a small enclosure that cannot grow conveniently.

Power and expansion planning

Four cameras require more than NAS drive capacity. Include the power and expansion requirements of the complete system:

• PoE switch power budget
• Camera night-vision or heater power, where applicable
• NAS power consumption
• UPS capacity and runtime
• Router and network-switch power
• Future camera ports
• Additional drive bays or an expansion enclosure
• Spare capacity for longer retention or higher bitrates

A UPS can provide time for an orderly shutdown during an outage, but it does not guarantee that cameras will continue recording indefinitely. If the PoE switch, network equipment, or cameras lose power, the NAS cannot record their streams.

Storage sizing checklist for four cameras

Use this checklist before buying a NAS or NVR:

• [ ] Record the average bitrate for each camera.
• [ ] Confirm whether the bitrate is average or maximum.
• [ ] Identify the codec used for recording.
• [ ] Decide between continuous, motion, or scheduled recording.
• [ ] Estimate motion duty cycle separately for each camera.
• [ ] Include audio if it is enabled.
• [ ] Set the required retention in days.
• [ ] Calculate daily storage using bitrate × 10.8.
• [ ] Add at least a practical allowance for metadata, filesystem overhead, and free space.
• [ ] Convert required usable capacity into raw capacity after RAID or ZFS redundancy.
• [ ] Check the NAS surveillance application’s camera support and licensing.
• [ ] Confirm camera, PoE switch, and NAS network capacity.
• [ ] Choose drives suited to the expected write workload.
• [ ] Decide whether the NAS will also run file sharing, Plex, backups, or other services.
• [ ] Plan UPS power for the NAS and network equipment.
• [ ] Define how footage will be backed up or exported.
• [ ] Leave room for additional cameras or longer retention if expansion is likely.

Once you know the required usable capacity and the NAS features you need, Browse NAS to compare suitable storage platforms. You can also review NAS and storage servers when surveillance is only one part of a broader home or small-business server setup.