How to Expand the Storage Capacity of a RAID

Posted on by Larry

A RAID is a collection of drives that act as a single storage unit.  It could include anywhere from 2 – 16 drives. We use them in video editing for their speed and capacity. However, given the size of video files, all too often these things fill up.

I have a 24 TB RAID which is almost full. This article describes what you need to know to expand the storage capacity of a RAID.


This shows HDDs in an enclosure.
(Image courtesy OWC.)



There are two types of storage which are used for a RAID. These are stored inside a box, called an “enclosure.”

SSD RAIDs are known for their extreme speed, but they don’t hold a lot. HDD RAIDs are slower, but hold far more and are easier to upgrade. While you can upgrade some SSD RAIDs, this article concentrates on HDD RAIDs.

NOTE: Contact the manufacturer of your SSD RAID to determine if it can be upgraded. If so, the process is the same.

There are two types of hard drives:

There are six “RAID levels” that are used to format a RAID.

You need to know which level your RAID uses because RAID 0 can’t be upgraded without first copying all data on the RAID to a different location, then replacing all the drives at once.

NOTE: Aside from RAID 0, all other RAID levels are designed to protect your data in case one drive dies. We are taking advantage of this “data redundancy” feature to remove a smaller drive and replace it with a larger capacity drive, then allowing the RAID to rebuild.

Not to worry, this isn’t a trick or dodgy workaround. It’s part of how RAIDs are designed. This is exactly what you would do to replace a drive that died.


(Image courtesy OWC.)

I own an OWC Thunderbay 4 (4-drive HDD RAID) with Thunderbolt 2 connectivity, so I contacted the RAID team at OWC and asked whether there was an advantage to replacing the Thunderbolt 2 enclosure with one using Thunderbolt 3?

OWC: There are additional benefits for daisy-chaining modern bus-powered accessories such as our Envoy FX. But for performance, no, there is little to no difference. Thunderbolt 2 is much faster than the drives, and if your enclosure is working reliably, it can continue for years. Make sure the Thunderbolt 3 to Thunderbolt 2 adapter you purchase is the Apple brand.

Larry: In other words, if I’m not connecting additional units into the back of the RAID, Thunderbolt 2 is just as fast as Thunderbolt 3 for HDD RAIDs holding 2-5 drives. Six or more drives, depending upon configuration, could reach the bandwidth limit of Thunderbolt 2. If you ARE connecting additional storage, upgrading to a Thunderbolt 3/4 chassis will improve performance.


Here’s how to calculate how much storage capacity to buy.


(Image courtesy: Matthais Zomer,

The actual upgrade is easy – thought it takes time – provided you are comfortable using a screwdriver. (This is identical to replacing a drive that failed.)

NOTE: It took me about four days to rebuild a four-drive RAID 5.

NOTE: You can use Apple Disk Utility to create RAID levels 0 and 1. OWC markets SoftRAID to create RAID levels 0, 1, 4, 5, 6 and 1+0. SoftRAID initializes and certifies drives. You would also use it to expand the capacity of a RAID.


(Image courtesy: Sergei Starostin,

When you buy a new RAID with drives, the manufacturer carefully matches the drives to the RAID.

But, when you buy replacement drives, you are on your own to figure out which drives are the best for your system. There are wealth of drives from Seagate, Toshiba, and Western Digital in a variety of colors and animals to choose from. If your goal is a system that provides performance with the capacity required for video editing, what type of drives should you pick?

So I asked OWC for suggestions. Their hard drive team wrote this:

LARRY NOTES: The problem with matching model numbers is that different capacity drives have different model numbers. So that won’t work. And trying to contact ANY drive manufacturer for drive advice is next to impossible.

Larry adds, here are other factors to consider when purchasing hard drives:

NOTE: Western Digital still does not make it easy to determine if a drive uses CMR or SMR technology, but this Western Digital blog explains how to find out.

(Image courtesy: Pixabay,


Back to my conversation with OWC.

Larry: Is there a speed difference between drives manufactured four years ago and ones manufactured today?

OWC: If you’re looking at the same family over multiple years there will be higher performance year-over year as new platforms are introduced. But some new drives that are released aren’t optimized to be “faster” and could, for example, be designed for reliability. We also work with our partners on newer hard drive firmware that can have improvements in performance.

Speed can also be affected by the technology of the drive you are using. SMR drives tend to get slower as they fill up. So a drive that is manufactured four years ago may have more pre-existing data on it than a drive that was just purchased today. This would result in a speed difference, since one already has data on it.

LARRY NOTES: This comment refers to the fact that as hard drives fill up, they slow down. In general, try to keep at least 20% free space on any HDD or HDD RAID.

Larry: How important is RPM – i.e. 7200, vs. 5400 vs. 10000 – for video editing, as opposed to small office documents or databases?

OWC: 10,000 is not as prevalent due to their cost, noise, and the introduction of SSD.

7200 will outperform 5400 at the same capacity and generation. Higher rotational speed means faster I/O, data rates which has benefits in both video editing (fast access) and databases (multiple users needing access at once). However, as density has gone up, performance has gone up, independent of RPM.

Larry: Does speed / bandwidth change as drive capacity get bigger?

OWC: As drives have evolved, there has been higher density per platter, which results in higher performance. But bandwidth is usually limited to the interface (SATA, M.2, etc.).

Larry: Does latency increase as drive capacity gets bigger?

OWC: No, generally not. Because as drives get bigger, they have gotten more dense, which has resulted in a net increase in speed.

Larry: What is the typical life expectancy of a RAID enclosure?

OWC: Hardware RAIDs tend to fail much quicker than software RAID systems because of their controller lifespans. Our software RAID enclosures tend to have a much longer lifespan and can evolve over time as technology changes.

We still have customers using arrays from over 10 years ago.

Generally, hardware raid systems are not supported software-wise past a certain period. This means that while the RAID box may work, the software to configure it (e.g. rebuild, monitor, upgrade) will not run on newer systems.

Many hardware RAID vendors also lock their systems down to specific drives. Over time, these drives become harder to find because they might not be manufactured anymore or might not have been sold on the conventional channel. This can mean that replacing a failed drive might be difficult, cost prohibitive, or even impossible to do. Our software raid, SoftRAID, and enclosures do not have any of these limitations.

Larry: What is the typical life expectancy of a hard drive in a RAID? (Granted this is harder to answer depending upon how it is used, but is there a range when we should consider replacing the drive?

OWC: As HDD drives approaches 5 years of age, it’s typically good practice to replace drives or only use them as a secondary source of storage. RAID or otherwise.

SoftRAID continually monitors drives and gives you a heads up months in advance if the there are signs of failure. This feature usually prevents our customers from getting to the point of an actual failure putting their data at risk.


It is generally possible to expand the storage capacity of an HDD RAID without buying a new enclosure; which can save hundreds of dollars. However, this is NOT true for RAID 0 devices, which don’t provide drive redundancy which makes this process possible.

To be safe, please check with the manufacturer of your RAID to see if they support replacing drives to upgrade capacity. I’ve done this successfully with OWC RAIDs and Synology servers.

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3 Responses to How to Expand the Storage Capacity of a RAID

  1. Saul says:

    Thanks for the info, Larry. Very helpful. Just one question you may be able to answer. hat is the maximun capacity that TunderbayBay 4 can hold? I mean, how big can be each disk? 12tb, even more?
    Thanks again!

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