How they differ
RAID 1 copies the same data to two drives: if one fails, the other keeps working. RAID 10 combines several mirrored pairs and spreads data across them, adding up the capacity and speed of every pair. It needs an even number of drives, at least four.
| Configuration | Usable capacity | Efficiency | Drives that can fail |
|---|---|---|---|
| RAID 1 · 2 × 8 TB | 8 TB | 50 % | 1 (the other mirror drive keeps going) |
| RAID 10 · 4 × 8 TB | 16 TB | 50 % | 1 per pair (2 only if in different pairs) |
| RAID 5 · 4 × 8 TB | 24 TB | 75 % | Any 1 |
| RAID 6 · 4 × 8 TB | 16 TB | 50 % | Any 2 |
Assumptions: equal drives, theoretical capacity before formatting and reserves.
How to read the table
RAID 10 and RAID 6 give the same capacity with four drives but behave differently. RAID 6 survives any two drive failures; RAID 10 only survives two if they are in different pairs, but in exchange it writes faster and rebuilds sooner. RAID 5 gives more space, yet after a failure it has no protection until the rebuild finishes.
When to choose RAID 1
On a two-bay NAS, RAID 1 is almost the only sensible option: the alternative, RAID 0, adds capacity but loses everything if one drive fails. RAID 1 is simple, either mirror drive can be read on its own in an emergency, and a rebuild just copies one drive to another.
Its limit is capacity: you always get the space of a single drive. To grow, you replace both drives with larger ones, one after the other, waiting for the rebuild to finish each time.
When to choose RAID 10
RAID 10 shines when speed matters, especially for writes: virtual machines, databases, video editing from the NAS or many users at once. With no parity to calculate, it writes faster than RAID 5 or RAID 6 and suffers less during a rebuild, because it only copies one drive from its partner.
The price is capacity: half the total, the same as RAID 6 with four drives but with lower fault tolerance. With six or eight drives, the space gap grows in favour of RAID 6.
Real speed depends on your network
A modern hard drive reads and writes at about 150-250 MB/s, while a 1 Gb/s network tops out around 110 MB/s. On a NAS connected at 1 Gb/s, RAID 1 and RAID 10 will feel almost the same when copying files: the network is the bottleneck.
The difference shows with 2.5 or 10 Gb/s networking, with several people working at once or with many small operations, such as those of a virtual machine. If your NAS only has a 1 Gb/s port, put capacity and safety before speed.
Rebuilds: the risky moment
When a drive fails and you insert a new one, the NAS rebuilds the data. With 8 TB drives, just copying one full drive at about 180 MB/s takes more than 12 hours, and in practice the process can last one or two days while the NAS is in use. Meanwhile RAID 1, RAID 10 and RAID 5 cannot tolerate another failure on the wrong drive.
That is why, with large drives and four bays or more, many administrators prefer RAID 6: it stays protected even if a second drive fails during the rebuild. If you can, buy drives from different batches so they do not age in exactly the same way.
If your NAS is a Synology: SHR
Synology offers SHR, a mode that works like RAID 1 with two drives and like RAID 5 with three or more, while making better use of mixed drive sizes and letting you grow by adding drives. SHR-2 is the RAID 6 equivalent. For home users it is usually the easiest option; RAID 10 is still better when performance is the priority.
Frequently asked questions
Does RAID replace a backup?
No. RAID protects against a drive failure, not against deletions, ransomware, a failure of the NAS itself or theft. Keep another copy outside the NAS as well, ideally following the 3-2-1 rule.
Can I move from RAID 1 to RAID 10 later?
It depends on the NAS. Many let you move from RAID 1 to RAID 5 by adding a drive, but converting to RAID 10 often means copying the data elsewhere and creating the volume again. Check your vendor documentation before you buy.
Which drives should I use in a NAS?
Drives designed for NAS use, such as the WD Red Plus or Seagate IronWolf ranges, built to run 24 hours a day in multi-bay units. Avoid SMR drives in RAID: their rebuilds can be very slow.