Organizing how to choose a NAS RAID configuration so beginners don't make mistakes

When you try to buy a NAS, you're often asked, "Do you want RAID 1 or RAID 5?" and many people freeze up at that point. Honestly, at first, it just sounds like a magic spell.

In this article, I will break down the types of RAID for beginners, keeping the math to a minimum.

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What is the purpose of RAID in the first place?

RAID is a mechanism that combines multiple HDDs to ensure that data is not lost even if one drive fails. Conversely, in a configuration with only a single HDD without RAID, there is a possibility that all data will be lost the moment that HDD fails.

However, there are different types of RAID, and the balance between the "range of protection" and "usable capacity" differs for each. If you buy without understanding this, you might end up with "less capacity than I thought" or "actually, there was no redundancy."

A casual explanation of typical RAID configurations

RAID 0: Zero redundancy, speed and capacity are the top priority

By distributing data across multiple HDDs, read/write speeds and usable capacity are maximized. However, if even one drive fails, all data is lost. It is absolutely not suitable for backup purposes.

RAID 1: Mirroring, the easiest and most reassuring design

The exact same content is written to two HDDs. Even if one fails, the data remains on the other, so it is safe. However, the usable capacity is only that of one HDD (only half of the capacity of the two drives can be used).

RAID 5: A balance of capacity and redundancy for 3 or more drives

A method that distributes data and "error correction information" across multiple HDDs. It can handle the failure of up to one drive and has better capacity efficiency than RAID 1. Requires 3 or more HDDs.

RAID 6: Can withstand the simultaneous failure of 2 drives

An evolution of RAID 5 that holds double the error correction information, allowing it to withstand the simultaneous failure of two HDDs. It is an option if you want to increase safety, but it requires 4 or more HDDs.

RAID 10: A combination of RAID 1 and RAID 0

This method writes data by mirroring pairs and then striping them. It offers excellent speed and redundancy, but requires at least four HDDs, and the usable capacity is half of the total installed HDD capacity.

Ultimately, which one should a beginner choose?

If using a 2-bay NAS (2 HDDs): RAID 1 is the only choice

For a 2-drive configuration, the practical options are only RAID 1 (mirroring) or RAID 0 (not recommended). If your goal is backup, choose RAID 1 without hesitation. The Synology DS224+ Review for small businesses is a representative example of a 2-bay model.

If using a 4-bay NAS (4 HDDs): RAID 5 is the practical standard

This configuration offers a good balance of capacity efficiency and redundancy, and is adopted by many homes and small offices. If you require higher safety, you can also consider RAID 6. The Synology DS925+ Review and QNAP TS-464 Review for medium-sized offices are representative examples of 4-bay models.

If using an 8-bay NAS (8 or more HDDs): RAID 6 or RAID 10

As the number of drives increases, the risk of multiple simultaneous failures also rises, so the dual redundancy of RAID 6 provides peace of mind. If speed is also a priority, RAID 10 is another option. The Synology DS1825+ Review for large capacity is an 8-bay model.

Why you shouldn't feel completely safe just because you set up RAID

RAID is only a safeguard against HDD failure. RAID alone cannot handle cases such as accidentally deleting files, being infected by ransomware, the NAS unit itself breaking, or damage from fire or water.

For truly important data, it is safer to prepare separate backups on external HDDs or in the cloud in addition to the RAID within the NAS.

Frequently Asked Questions (FAQ)

Q1. Can I change the RAID configuration later?
A. Support varies by product, but many NAS devices support changing the RAID level (migration) when adding HDDs or expanding capacity. However, since the process involves time and risk, it is safer to choose a configuration that suits your needs from the start.

Q2. If I'm unsure, should I choose RAID 5 or 6?
A. RAID 6 is often better for business use where data importance is high, while RAID 5 is sufficient for personal use or relatively light applications. Since recovery (rebuild) takes longer as the capacity of the installed HDDs increases, RAID 6 is safer when using large-capacity HDDs.

Q3. How much usable capacity is lost when setting up RAID?
A. RAID 1 and RAID 10 use half of the installed capacity, while RAID 5 uses the equivalent of one HDD for redundancy. For example, in a RAID 5 setup using four 4TB HDDs, the actual usable capacity will be around 12TB (varies by configuration and product).

Q4. What kind of HDDs should I use?
A. It is recommended to use NAS-specific HDDs (such as WD Red or Seagate IronWolf) designed for 24/7 operation. Standard PC HDDs are not designed for continuous operation, which may increase the risk of failure.

Q5. Is it okay to use it without setting up RAID?
A. Configurations that simply bundle HDDs to increase capacity (such as Basic or JBOD) have no redundancy, so a single failure will lead to immediate data loss. This is not recommended if you are handling important data.

Q6. Can another HDD fail during a rebuild (recovery process)?
A. It is possible. Since other HDDs that have been running for the same amount of time as the failed one may also be near the end of their lifespan, the risk of an additional failure during a rebuild is not zero. This is another reason not to rely solely on RAID.

Summary | Once the number of bays is decided, the RAID options naturally narrow down

RAID configuration may seem difficult, but in reality, once you decide on the number of NAS bays (how many HDDs it can hold), the available configurations are significantly narrowed down. For 2 bays, RAID 1 is the realistic standard; for 4 bays, RAID 5 or 6; and for 8 bays, RAID 6 or 10.

Also, please do not forget that just because you have set up RAID, it does not mean you are completely safe; you still need separate backups for accidental deletions, ransomware, and hardware failures.

Since this is a significant investment, I recommend comparing options rather than making an immediate decision. By first saving items to your Amazon cart, you can carefully compare the number of bays, capacity, and intended use.

▼ Save to cart first and compare carefully

For how to choose based on scale, please also see [Complete Guide to Choosing a NAS], and for the difference in usage between a NAS and an external HDD, please see [Comparing NAS and External HDD Differences].