Learn the Basics Behind Every NAS Drive Choice
Four ideas explained once, so the model pages can stick to the model
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Four ideas sit behind every drive recommendation on this site. Use CMR drives in an array, because SMR drives rebuild slowly. Use NAS-rated drives, because they are built and warrantied for continuous running in a multi-drive enclosure. Know what your redundancy layout costs in drives before you buy. And check the maker's own compatibility rules for your exact model, because they differ. The model pages assume all four and do not repeat them.
CMR and SMR
The two terms describe how a hard drive lays down tracks. A CMR drive writes tracks side by side. An SMR drive overlaps them like roof shingles to fit more on a platter, which means rewriting one track disturbs its neighbours and the drive has to tidy up afterwards.
That tidying is invisible when you copy the odd file and painful when an array rebuilds, because a rebuild is one long sustained write. Every table of NAS drives on this site is restricted to CMR models for that reason.
The longer version
The CMR and SMR page goes through which drive lines use which method and how to check a model.
NAS-rated drive or desktop drive
| NAS-rated drive | Desktop drive | |
|---|---|---|
| Designed for | Running all day in an enclosure with other drives | A single drive in a PC, used part of the day |
| Error recovery | Gives up on a bad sector quickly so the array can repair it | May retry for a long time, which an array can read as a failure |
| Vibration | Higher-capacity lines carry sensors to cope with neighbouring drives | Usually none |
| Warranty | Covers use in a NAS | May exclude it; check the terms |
Where enterprise drives fit
Enterprise lines are built for the same continuous use at higher workloads, and in 2026 they have often been the cheapest new drives per terabyte at high capacity. They are louder and draw more power. For a NAS in a living room that matters; in a cupboard it does not.
What redundancy costs, in drives
| Layout | Fewest drives | Drives given to protection | Survives |
|---|---|---|---|
| Mirror (RAID 1) | 2 | Half | One failure per pair |
| Single parity (RAID 5, SHR, RAID-Z1) | 3 (SHR: 2) | 1 | One failure |
| Dual parity (RAID 6, SHR-2, RAID-Z2) | 4 | 2 | Two failures |
| Striped mirrors (RAID 10) | 4 | Half | One failure per pair |
What SHR is
Synology Hybrid RAID is Synology's automated RAID management system. Classic RAID sizes a pool by its smallest drive, so larger drives in the same pool are partly wasted. SHR divides each drive into smaller chunks and builds extra redundant storage from them, so it can use capacity that classic RAID leaves idle.
It also grows more easily. Classic RAID cannot expand a pool until every drive has been replaced with a larger one; SHR can expand as soon as two drives have been upgraded. SHR with one drive of protection needs at least two drives, and SHR-2, which survives two failures, needs at least four.
SHR exists only on Synology, and Synology notes that some of its models do not support it or support it only in part.
Checked on October 12, 2026. Sources: Synology Knowledge Center: What is Synology Hybrid RAID (SHR)?.
Compatibility lists are per model
A maker's list of tested drives is published per model, and what happens to a drive that is not on it differs by maker and by generation. On most NAS an unlisted drive simply works. On Synology's 2025 models the rules are written down and stricter for M.2 drives.
So the order of checks is always the same: the model's own page first, then the price table.
Synology's current rules
What DSM 7.3 allows on 2025 models, and what it still blocks, has its own page.
NAS-rated CMR drives, by price per TB
Renewed, refurbished and used listings
Shown for reference. These are not counted in the best price per TB above, and warranty terms differ from new drives.
Frequently asked questions
Do I really need NAS drives in a NAS?
For an array that runs all day, yes. They are designed and warrantied for it, and their error-recovery behaviour suits RAID. A desktop drive can work for a single-drive backup target.
Is SMR ever acceptable in a NAS?
For a single drive that is written occasionally, it can be. In a parity array it makes rebuilds slow, so every NAS drive table here excludes it.
Is SHR better than RAID 5?
Both survive one drive failure. SHR is the better choice if you expect to mix drive sizes or to grow by swapping in larger drives, because it can use space classic RAID leaves idle and can expand after two drives are upgraded.
How many drives do I lose to redundancy?
One with single parity, two with dual parity, half with mirrors. That is whole drives, whatever their size.
Does a compatibility list mean other drives will not work?
Usually not. It means those drives were tested. Whether an unlisted drive is blocked depends on the maker and model, which is why each model page states its own rule.
Should I use RAID 5 or RAID 6?
RAID 6 is the conservative default for six large drives because it tolerates two failures. RAID 5 returns more capacity but leaves less margin during a long rebuild.
Can a portable USB SSD go in a NAS drive bay?
No. A portable SSD is an external USB device. Use a bare 2.5-inch SATA SSD for an internal SATA tray or an M.2 2280 NVMe for the M.2 slot.
Why is usable capacity less than the total of the drives?
Two things reduce it. Redundancy hands one drive (or two for RAID 6 and SHR-2) to fault tolerance so the array survives a failure. Then drive makers count 1TB as a trillion bytes while the operating system counts in binary and the filesystem reserves a little, so real usable space is about 91 percent of the raw figure.
Does SHR or RAID replace a backup?
No. SHR keeps service running through a drive failure; it does not protect against deletion, ransomware, theft or enclosure failure. Keep another copy.
Are NAS-rated SSDs worth it over ordinary SSDs?
For a NAS that runs continuously, NAS-rated SATA SSDs have higher endurance ratings and firmware tuned for RAID. For light home use a good consumer SATA SSD also works, but check the TBW endurance figure before buying.
Does more RAM speed up a NAS?
It speeds up metadata-heavy and multi-tasking workloads (containers, VMs, photo indexing, many users) rather than raw sequential transfer, which is limited by the drives and the network. Add RAM before an SSD cache for most home setups.
Do I need a high-endurance NVMe drive for cache?
For a write cache that runs 24/7, a drive with a higher TBW rating lasts longer than a budget consumer drive. For a read-only cache or a light load, a mainstream DRAM NVMe is acceptable.
Is an NVMe cache or more RAM the better upgrade?
Add RAM first if you can: it is cheaper and helps metadata and many small operations. Add an NVMe cache when your active data set is larger than the RAM but you still want fast access to it.