Buying a NAS for today's needs is the most common sizing mistake. A NAS is infrastructure, not a consumable. The hardware you choose today will likely outlast three or four generations of drives, two or three operating system versions, and a significant shift in how much data you generate. Planning only for current needs leads to either undersized hardware that limits your upgrade path, or oversized hardware you pay for but cannot fill. The right approach is to plan for the hardware lifecycle and the data growth curve separately.
In short: Buy more bays than you currently need - the hardware cost difference is small and the upgrade flexibility is large. Start with fewer drives than the NAS can hold, add drives as data grows, and replace drives based on health, errors, warranty status and capacity needs rather than a universal age threshold. Over 10 years you will likely span two NAS hardware generations; plan the transition point now rather than being forced into it.
How Fast Data Actually Grows
Data growth rates vary enormously by use case. The biggest planning mistake is using a rule of thumb that does not match your actual workload. Estimating growth based on current consumption rather than the specific categories of data you generate leads to capacity plans that are either too conservative or wasteful. For product recommendations, see our best nas.
Illustrative annual data-growth scenarios by use case; these are planning assumptions, not measured typical rates
| Conservative (low growth) | Moderate (typical home) | Active (heavy user) | |
|---|---|---|---|
| Documents, email archives | 5-10% per year | 10-20% per year | 20-30% per year |
| Photo library (JPEG/HEIC) | 10-15% per year | 20-30% per year | 40-60% per year |
| Photo library (RAW files) | 20-30% per year | 50-100% per year | 100-200%+ per year |
| 4K video (personal/family) | 10-20% per year | 30-60% per year | 100%+ per year |
| 4K video (professional/production) | 100% per year | 200-400% per year | 400%+ per year |
| Surveillance footage (retained 30 days) | Stable (rotation) | Stable (rotation) | Stable (rotation) |
| VM and container storage | 20-50% per year | 50-100% per year | 100-200% per year |
| Music library | 0-5% per year | 5-15% per year | 5-15% per year |
The practical exercise: calculate your current total data volume, identify which categories are growing, and apply the relevant growth rate to project forward. A 4TB photo and document library growing at 30% per year doubles in approximately 2.6 years, reaches 4x in about 5 years, and is at 16x in roughly 10 years. That same library at 10% per year grows to only 2.6x in 10 years. The planning implications are completely different.
Video can be a major growth category for households that regularly retain 4K footage or local media libraries, but the dominant category depends on the household's workload. Photo and video sync can increase NAS use when users automatically retain content from higher-capacity phones.
The Two Hardware Cycles to Plan Around
Over a 10-year horizon, you are planning around two distinct hardware cycles: the NAS enclosure cycle and the drive cycle. These have different timelines and different cost profiles.
NAS enclosure replacement has no universal interval; use the model's support status, hardware health, capacity and performance requirements to determine timing. The NAS hardware - the enclosure, motherboard, processor, RAM, and network ports - typically remains functional for 7-10 years in a home or small business environment. The main reasons to replace the enclosure before end of mechanical life are: the software platform reaching end of support, insufficient RAM for new OS features, inadequate network speed for upgraded infrastructure, or the enclosure reaching its maximum drive capacity before data growth does.
Drive cycle: approximately 4-5 years. NAS-drive replacement timing varies; base it on health indicators, errors, warranty or service policy, workload, capacity needs and the available backup and redundancy protections. Available drive capacities and prices change over time, but neither a fixed annual capacity-growth rate nor similar future prices should be assumed. This creates natural replacement opportunities that can expand total NAS capacity without requiring a new enclosure.
Over 10 years: plan for one enclosure purchase and two drive generations. The first drive generation fills the starting bays. The second generation replaces those drives with higher-capacity models, potentially doubling usable storage at the same bay count or higher. If the enclosure has empty bays, adding drives in between generations gives additional flexibility.
Choosing the Right Starting Bay Count
The bay count decision is primarily a question of how many incremental upgrade steps you want available before being forced to buy a new enclosure. More bays give more upgrade paths. The hardware cost difference between bay counts is much smaller than most buyers expect relative to the flexibility gained.
| 2-bay NAS (e.g. Synology DS225+, ~$528) | Maximum 2 drives. No room to add drives. On a non-expandable 2-bay NAS, capacity growth generally requires replacing member drives or migrating to another NAS; some models support compatible external expansion units. Suitable only when the projected dataset fits the usable capacity of the selected two-drive RAID or SHR configuration. |
|---|---|
| 4-bay NAS (e.g. Synology DS425+, ~$848) | Start with 2 drives, add 2 later. RAID 5/6 available. Starting with two drives leaves up to two drive-addition steps, subject to the RAID type and drive-size requirements. Suitable when the projected dataset fits the usable capacity provided by four bays under the selected RAID configuration. |
| 5-bay NAS (e.g. Synology DS1525+, from approximately $1,600 AUD) | More flexible upgrade path. SHR scales well across odd numbers of drives. Good for prosumers and growing media libraries. |
| 6-bay and above NAS | Multiple incremental upgrade opportunities. RAID 6 efficiency improves at higher bay counts. Better suited for small business or production data that will grow substantially. |
The price difference between a 2-bay and a 4-bay NAS with similar hardware specs is approximately $250-350 AUD at current market pricing. Over a 10-year horizon, that difference is negligible compared to the flexibility gained. The argument for starting with a 4-bay over a 2-bay is almost always correct unless the dataset is definitively small and stable.
The Drive Upgrade Path Over Time
A well-planned NAS drive upgrade cycle looks like this:
Year 0: Initial purchase. Fill 2 bays of a 4-bay NAS with the capacity you need now. Leave the other 2 bays empty. The cost is lower and you are not paying for capacity you cannot use immediately.
Year 2-3: Capacity expansion. Add 2 drives to the empty bays. The NAS OS expands the storage pool to include the new drives. Adding drives starts a storage-expansion or resync operation whose duration varies with data size and system load; do not interrupt it, and maintain a separate backup. You now have 4 drives and significantly more usable capacity.
Year 4-5: First drive generation replacement. The original 2 drives are now 4-5 years old. Drive capacities have increased since purchase. Replace the original drives one at a time with larger drives. Each replacement requires a rebuild, but only one drive is out at a time. Whether capacity can be expanded after two replacements depends on RAID type: equal-sized SHR-1 needs at least two larger drives, SHR-2 at least four, while conventional RAID requires replacing all equal-sized member drives. The newer drives (added in year 2-3) are still within their normal service life.
Year 7-9: Second drive generation replacement. The year-2-3 drives are now 4-6 years old. Replace these with the then-current large-capacity drives. By this point, larger compatible drives may be available, but the capacity increase cannot be predicted reliably in advance. The same 4-bay enclosure now holds substantially more data than at year 0.
This staged approach means you are never replacing all 4 drives at the same time, never paying for capacity you do not need yet, and always have SMART monitoring data on drives of different ages to detect problems early.
When to Replace the NAS Enclosure
The NAS enclosure should be replaced when one of the following conditions applies, not on a fixed schedule:
Software end of support. Vendor support information is published in different formats; check the exact model's current support-status page rather than assuming a fixed end-of-support timeline. Once a model drops off the supported list, it stops receiving DSM or QTS updates, which has security implications for any NAS accessible from the internet. Plan the enclosure replacement around this date, not around the hardware's mechanical life.
Network speed bottleneck. If your home or office network has moved to 10GbE or higher and the NAS has only a gigabit port, the NAS becomes the network bottleneck. Gigabit Ethernet is limited to approximately 125MB/s. If your primary workflow involves moving large files (video, VM images) between workstations and the NAS, 10GbE matters. The Synology DS925+ has two built-in 2.5GbE ports and no 10GbE upgrade slot. Older models would require a PCIe expansion card, which is available for some platforms but not others.
Capacity limit reached before data growth ends. If you have filled all bays and replaced all drives with the maximum available capacity, and data continues to grow, you need a larger enclosure. Planning for this means choosing an enclosure with more bays than you currently need so this point is as far in the future as possible.
CPU or RAM no longer adequate. Transcoding, AI photo indexing, running containers and VMs simultaneously - these workloads push older NAS hardware. A NAS running Synology Photos AI, Plex transcoding, and four containers simultaneously on a 2016-era Realtek processor is a different experience from the same workload on a modern AMD or Intel N-series chip. If performance becomes a consistent friction point, the hardware is due for replacement.
A 10-Year Planning Framework by Use Case
Recommended starting configuration by use case (10-year horizon)
| Home (light use) | Home (active media) | Home lab / prosumer | Small business | |
|---|---|---|---|---|
| Starting bay count | 2-bay acceptable | 4-bay recommended | 4-6 bay | 4-8 bay |
| Starting drive count | 2 (full array) | 2 of 4 bays | 2-4 of available bays | 4 minimum |
| Starting drive size (approx.) | 4-6TB | 6-8TB | 8-12TB | 8-20TB |
| Initial RAID configuration | RAID 1 or SHR | RAID 1 or SHR | SHR / RAID 5 (consider SHR-2 at 8TB+) | RAID 6 / SHR-2 |
| First expansion trigger | >80% full | >70% full or year 2-3 | Year 2-3 or when needed | Year 1-2 |
| Enclosure replacement horizon | 8-10 years | 7-9 years | 6-9 years | 5-7 years |
| Example hardware (2026) | DS223 or DS225+ | DS425+ or DS925+ | DS925+ or QNAP TS-464 | DS1525+ or QNAP TS-664 |
Australian Buyers: What You Need to Know
Drive pricing and availability in 2026. Current NAS-drive pricing varies by capacity, model and retailer; compare live Australian prices rather than assuming a uniform increase from 2024-2025. Planning an incremental upgrade approach means spreading drive purchases over several years, which hedges against current elevated pricing. Buying all drives at once to fill a NAS at today's prices locks in the current premium. Buying half now and adding more in 2-3 years uses capital more efficiently and may benefit from improved pricing if supply constraints ease.
Synology software support timelines. Synology has improved its support lifecycle transparency in recent years. Synology currently lists the DS225+, DS425+, and DS925+ as having Full DSM update status, but its product-status page does not publish model-specific end dates for them. QNAP maintains a separate model-specific Product Support Status system; check the exact model rather than assuming that its lifecycle matches Synology's. Factor end-of-support dates into any 10-year plan - particularly for NAS devices used in business contexts where security updates are non-negotiable.
Local warranty and service. For in-warranty QNAP products, QNAP directs customers to the original reseller or vendor; Synology also directs replacement cases through the local reseller or distributor. Confirm the applicable process with the seller before purchase. Buying from a specialist retailer like Scorptec or PLE rather than Amazon or a generalist marketplace gives you better access to the distributor support chain when that point arrives.
NBN and remote backup planning. If your 10-year NAS plan includes cloud backup as an offsite copy, account for the realities of Australian NBN upload speeds when sizing the backup dataset. A 30TB initial backup over a 20Mbps upload connection would take months at the theoretical line rate; current NBN upload speeds vary by access technology and plan. The practical approach is to define which data is business-critical or irreplaceable and prioritise that for cloud backup, rather than attempting to replicate the entire NAS offsite. Raw video archives and surveillance footage can be excluded from cloud backup while photos, documents, and irreplaceable files are protected offsite.
Free tools: NAS Sizing Wizard and Backup Storage Calculator. No signup required.
Related reading: our NAS explainer.
See also: our complete Synology NAS Australia guide.
How much storage should I buy for a new NAS?
Start with twice your current data volume as usable storage, not your current data size. This gives you room to grow without immediate pressure to expand, and a comfortable fill level to maintain NAS performance (performance and maintenance effects at high utilisation depend on the filesystem, workload and NAS platform). If you have 3TB of data, a 6TB usable RAID configuration (two 8TB drives in RAID 1 gives you 8TB usable) is a reasonable starting point that leaves room for growth before the next expansion decision.
Can I mix old and new drives in a NAS?
Yes, with caveats. Mixed-capacity support and usable capacity depend on the NAS platform and RAID type. Synology SHR supports mixed capacities subject to drive-size requirements; conventional RAID capacity is constrained by the smallest member drive. , and the reliability of an older drive in the same array as newer drives means the older drive's failure probability affects the whole array's rebuild risk. Gradual replacement of older drives with newer, larger models is a common and supported upgrade path.
What happens to my data when I replace drives with larger ones?
The process depends on the RAID level and NAS platform. In Synology SHR or RAID 5/6, replacing drives one at a time with larger ones triggers a rebuild after each replacement. The number of larger-drive replacements required before capacity can expand depends on the array: equal-sized SHR-1 requires at least two, SHR-2 at least four, while conventional RAID with equal-sized members requires replacing all member drives one at a time. On models that support hot-swapping, the replacement process can remain online; otherwise each physical drive replacement requires a shutdown. The full expansion process across 4 drives can take several days due to multiple sequential rebuild cycles.
Should I buy a NAS with a PCIe expansion slot for future-proofing?
Network expansion is model-specific: the QNAP TS-464 supports optional 5GbE or 10GbE through its PCIe slot, while the Synology DS925+ has no network-upgrade slot. Synology's DS1825+ is one model that supports optional 10/25GbE. For buyers who are currently on a gigabit network but anticipate upgrading to 10GbE in the next few years, a PCIe expansion slot is genuine future-proofing. For buyers with no near-term plans for higher-speed networking, the slot adds cost without benefit. The Synology DS925+ has two built-in 2.5GbE ports and does not support a 10GbE expansion card.
Is it worth buying a 6-bay or 8-bay NAS for a home setup?
For most home users, a 4-bay NAS provides sufficient upgrade headroom for a 10-year horizon. A 6-bay becomes worth considering if the primary use case is professional video production, surveillance with multiple cameras, or homelab workloads that require dedicated pools for different data types. An 8-bay home NAS is usually more hardware than a single household needs, though the Synology DS1825+ (8-bay, ~$1,899 AUD) is a legitimate choice for prosumers running large media libraries alongside VMs and containers.
How much does running a NAS cost in electricity over 10 years?
A 4-bay NAS with four spinning NAS-grade drives draws approximately 25-40W at idle. At the Australian average electricity rate of approximately $0.28-0.35/kWh (varying by state), a NAS running 24/7 costs approximately $70-110 AUD per year in electricity. Over 10 years, that is $700-1,100 in electricity costs. This is worth factoring into total cost of ownership, particularly when comparing a NAS to cloud storage subscriptions. The NAS power cost represents a meaningful ongoing expense, though it is typically lower than the subscription cost of equivalent cloud storage at Australian cloud provider pricing.
Once you have a capacity plan, the NAS buying guide covers the current models across Synology, QNAP, Asustor, and UGREEN with AU pricing and availability, so you can match the right hardware to your 10-year plan.