If you need to expand your Mac storage in a big way without breaking the bank, your best bet is with external hard drives. Here’s everything you need to know about hard drives and enclosures to put them in.

Storage can be a pain point for computer users. Apple’s famously expensive storage upgrade fees can put off users from adding more capacity from the outset, leaving them constrained until their next upgrade.

This is a solvable problem.

Cloud storage is always an option, especially if you’re sharing files between a Mac and an iPad or iPhone. But, considering ongoing costs associated with cloud storage, along with the need for Internet access, it isn’t the best result.

Apple’s design decisions have made it almost impossible for the average user to physically change the storage inside of a Mac.

There is also the often-chosen route of using network-attached storage (NAS) for expansion, and it is especially useful when dealing with multiple users. However, connecting over the network isn’t necessarily fast and responsive enough for some users.

For speeds in between network-attached storage and SSDs, there’s the tried and true hard drive with a direct-attached storage enclosure.

Hard Drive over SSD

At face value, there are advantages to using an SSD over a hard drive. As the newer drive that uses electrical impulses and chips for storage, the SSD can operate much faster than a hard drive.

A traditional hard drive, which uses treated platters spun at high speed within a casing, operates much more slowly. Like a record player or a CD, a read head has to physically move into position above a spinning layer, so that it can read or write to tracks.

With claims of platter rotation speeds of 5,400 rotations per minute (RPM) or 7,200 RPM, these drives sound like they can be fast. However, the reliance on moving parts means these drives are very slow versus the electrical impulse-based SSD or NVMe drive.

Examples of a hard disk (left) and an SSD (right)

There is a considerable speed difference, in that a typical SATA hard disk could access data at around 75-150MB/s. An SSD, on the other hand, will operate at much faster speeds, from 300MB/s going into gigabytes-per-second territory.

The flash memory-based SSD also has other benefits, including reliability, since there are no mechanical parts. By contrast, moving or knocking a hard drive while it is spinning up to read data can potentially damage the tracks on the platters.

Mechanical drives also have the extra shortcoming of sound. Since a hard drive uses a motor to spin the platter around, this generates noise and vibrations that the user could hear and feel.

SSDs simply don’t have these drawbacks at all, since they operate silently and without any moving parts.

Disk fragmentation is also an issue that SSDs don’t come across. Over time, as you create and delete files on a hard drive, you may run across a problem where files are fragmented and spread widely across the drive, instead of being optimally next to each other on the platter.

To solve this, computers would defragment the drive, shuffling parts of files around to bring them next to each other on the platter. This eliminates the situation of a drive repeatedly having to seek lots of smaller parts across physical space, increasing the time it takes to retrieve the file.

While an SSD could feasibly be "fragmented," the way SSDs work and the speed of access mean it isn’t really a problem for modern users.

Ultimately, a hard drive is slower, louder, more sensitive to movements, and can be affected by fragmented files, while an SSD is faster, silent, and much more resilient.

These are good reasons to use SSDs instead of hard drives, but the older drive technology does have one considerable advantage: cost. When looked at on a cost per terabyte or per gigabyte basis, a hard drive is considerably cheaper than an SSD, especially at higher capacities.

A reasonably-priced 4-terabyte SSD could cost a person over $260, or $65 per terabyte of capacity. However, you could get a 4-terabyte hard drive for $80, or $20 per terabyte.

There’s also the sheer capacity of hard drives to consider, which can be acquired at high amounts, such as 30 terabytes on the consumer level. You can get very-high-capacity SSDs, but be prepared to pay over four figures for the privilege.

SSD is certainly the way to go when you are thinking about adding storage to a device like a MacBook Pro that’s always on the move. In most cases, it’s the best option.

However, if you need a lot of sheer storage capacity without needing to worry about drive noises or physically moving the drives around, at the lowest cost, a hard drive-based system is the better way.

Drive types

The common hard drive is sold in 3.5-inch and 2.5-inch casings, with the former intended for larger devices and the latter for slimline notebooks of yesteryear. Functionally, they are the same, but you’ll find the physically larger drives are cheaper, faster, and can be found in higher capacities.

Consumer hard drives will connect using SATA (Serial ATA), a bus type that has been around for decades. There are others, such as SCSI and Serial Attached SCSI (SAS), but the vast bulk of consumer drives will be SATA in nature.

It is advised that, unless you have a very specific reason for doing so, you should avoid buying SAS or other drive types. SATA is the standard for this style of enclosure, and others won’t work.

A stack of 2.5-inch hard drives.

It’s not as fast as newer connection types, like the hyper-speed PCIe used by NVMe drives. But at the same time, the appeal of these drives is the capacity, not blistering speed.

Hard drives chatter and are noisier than SSDs. Drives spin, read/write head moves, and so forth.

The noise itself will vary between models, with different rotation speed ratings for the drive translating into volume and pitch of noise, as well as different access speeds for data.

A 7,200RPM drive will generally be noisier than a 5,400RPM drive, but it will be able to access files a little bit quicker.

Caches

To help improve the speed of a hard drive, manufacturers tend to include a disk cache or disk buffer. This is a very small amount of SSD-style memory on the physical drive, which is used as an intermediary between the data on the spinning platters and the computer system trying to access it.

More extreme versions can be referred to as "hybrid" drives or SSHDs. These include a lot of SSD storage on the drive alongside the spinning platters, and are marketed more openly as a way to have the best of "both worlds" of SSD and hard drives.

The buffer can be used to cache frequently-accessed data in some cases, but the real benefit is for write speed. Rather than wait for the read heads to write data to the thin layers of rust on the platters inside the drive, the buffer can take some of that data and store it.

For the computer, it speeds up the write time since the data is on the drive in some way. For the drive, it gives the computer the illusion of speed, but gives it a chance to continue writing the data to the platters in its own time.

Drive categories

While you will find a variety of capacities and speeds for hard drives on the market, you’ll also find a variety of hard drives. Though they ultimately function the same way, they are usually tweaked to best suit different use cases.

Beyond your typical hard drive, you will encounter "enterprise" drives, which are high-performance and high-reliability versions designed for business use. Think servers for business-critical tasks.

There are also Network Attached Storage drives, which are designed to work in close quarters with other drives for long periods of time. They are usually made to be more durable than a typical hard drive when it comes to handling vibrations.

These drives are also intended to be used in an always-on state, versus the more intermittently-accessed consumer drives.

This category of drives also tends to include versions marketed for surveillance system use.

For end users, the general advice is to stick with consumer drives for a single-drive external storage assembly, unless you use one with multiple drives in close proximity. In which case, switch to NAS drives.

Drive CMR, SMR and HMR

The way that hard drives read and write data can greatly affect the capacity. With newer technologies being developed, the capacity of high-end drives goes up, making them even more useful for storage.

Conventional Magnetic Recording (CMR) or Perpendicular Magnetic Recording (PMR) is the usual method of writing tracks on most hard drives. Tracks are written directly to the thin layer of magnetically affected material on top of each spinning platter of a hard drive.

The key here is that, like a record player, the tracks are recorded without overlapping. However, this approach uses up the most physical space on the platter’s surface.

A hard driver platter is designed to spin and be read with a moving arm. Like a high-RPM record player.

A second method is Shingled Magnetic Recording, which overlaps data tracks slightly, like shingles on a building’s roof. This method means more data can be squeezed onto a platter than under CMR.

However, due to tracks overlapping other tracks, the approach can make it harder to write new data to the platter. There is the possibility of having to rewrite previously overlapping tracks when data is changed, which can significantly decrease the writing speed of drives.

Heat-Assisted Magnetic Recording (HMR or HAMR) is a new technique that can help speed up writing data by heating up the platter. Using a laser, the part of the platter that is being written to is heated up, which makes it more receptive to writing data.

This method can be used to fine-tune exactly where data is written, which can improve accuracy for writes. It can also enable drives to pack tracks more densely together.

On the bleeding edge are drives that combine together SMR and HMR, namely creating narrower tracks that are "shingled" with an overlap. This has been used to create some extremely high-density hard drives, but at a premium.

Enclosures: Drive or DAS

While the kind of drive is one thing to consider, you also have to think about what you’re putting them into. With the exception of outliers such as hard drive docks, your typical enclosure choice falls into a few categories.

The primary one is a drive enclosure. Generally built to hold one drive, it is a very simple way of attaching storage to a Mac. Since it is very simple to use one drive and one enclosure, it’s also the cheapest method.

Doing so won’t give you any benefits of multi-drive enclosures, but it is cheap and often the most compact, and therefore the better option for portability.

That said, we have seen the rise of hubs and docks with built-in storage. This provides the benefit of external storage capacity while also providing more ports for the user, often at the expense of bandwidth.

DAS and RAID

A second category is for multi-drive enclosures, often referred to as Direct Attached Storage (DAS). This is effectively a single-client Network Attached Storage (NAS) that is directly connected, not via a network.

Since it holds multiple drives, this gives some considerable benefits over a single-drive system. First, more drives can mean more total storage capacity for your files.

Then there are the advantages of RAID (Redundant Array of Independent Drives), a way of controlling how the drives function and how data is stored. There are different levels of RAID, which provide different benefits.

A DAS can have a lot of drive bays for many, many drives

RAID 0 is a "Striping" layer, in that data is split across multiple drives, so two halves of a file could be stored on separate drives. This can result in faster access to files and speedier writes, with both drives handled as a single large data store.

The disadvantage here is a lack of redundancy, as if you lose one drive, you functionally lose all the data on both drives.

An alternative to this is RAID 1, "Mirroring," which writes the same data to two drives. You don’t get the speed benefit of RAID 0, and you also lose total capacity for your data.

Crucially, the mirroring means your data is safer if one drive fails, since the other will still have a copy.

If you have more than two drives in a DAS, you can use other forms of RAID, including RAID 5, which combines Striping with Parity. Data is stored in sections across multiple drives, with one of the sections consisting of a parity bit.

If you were to lose one of the drives, the remaining data and the parity bit can be used to calculate the missing drive’s data, rescuing the backup.

RAID 5 does reduce the total overall data capacity of the drives, but not in half like RAID 1.

RAID 6 is the same as RAID 5, except two parity bits are used, not just one. This means two drives from a collection of four could simultaneously go wrong, but the data is still usable and safe.

At the high end is RAID 10, which combines mirroring and striping from RAID 0 and RAID 1. It’s a costly way of having redundancy as it halves your total capacity, and is doable in Disk Utility, but it still provides the speed benefits of striping.

Depending on the DAS you pick, it could include RAID 0 and 1, or it could support RAID 5, 6, and 10 in software or hardware.

Within macOS, you can use Disk Utility to create a RAID disk set. The options, under the File menu under RAID Assistant, can configure drives in striped RAID 0 and mirrored RAID 1 setups. RAID 10 can be made by making two RAID 1 setups, then combining those in RAID 0.

It can also handle a third drive type, Just a Bunch of Drives (JBOD), which combines all of the drives into one large storage pool.

While useful, Disk Utility does not include native support for creating RAID 5 arrays. For that, you will have to turn to third-party applications.

One example is OWC SoftRaid, which can configure a set of drives in RAID 0, 1, 4, 5, and 10. It also has features like drive failure monitoring, as well as support for Apple HFS+ and APFS file systems in Windows.

There is a free version of SoftRAID available for reading existing volumes outside of RAID 5, which can be read and written natively by macOS, but you would need to pay $149.99 for a one-year subscription to create volumes.

A DAS with many drive bays also provides an extra opportunity for speed, beyond striping across drives. There is sometimes the option of installing an SSD into one of the drive bays, which can provide faster storage than a hard drive.

Some DAS units also have the option for M.2 storage alongside the main drive bays. This again could be used to help cache files for faster writes, or to hold most-used files or those you wish to access quicker than you would do through normal drive access.

What about a NAS?

Using a NAS is entirely a possibility for data storage. Like a DAS, it is a device that can hold a bunch of hard drives, complete with RAID support.

However, while a DAS is directly connected up to your Mac, a NAS is accessed through your network, hence the name Network Attached Storage.

There are benefits to this approach, such as being able to be accessed by multiple devices on a network, not just your lone Mac. For sharing files in a group, such as with family members at home, a NAS may be a better way forward than directly attached storage.

Other benefits include the NAS typically having other network services, such as acting like a streaming server for Plex. There’s also the benefit of having a box of noisy drives being in a physically different part of a home or office, out of earshot.

However, a DAS does still have the advantage of connection speed. A typical Gigabit Ethernet network will be a lot slower than a direct USB 3 connection by a wide margin, let alone USB 3.2 Gen 2 or Thunderbolt.

If it’s being used for Time Machine backups, it doesn’t matter which you go for, but they’ll be quicker with the DAS. In fact, just about everything will be a tad quicker using a DAS instead of the NAS.

Each approach has its benefits, but for this article, a NAS is being treated separately.

Connectivity

Regardless of if you use a single drive, a hub or dock with storage, or a DAS, you have to connect it to your Mac in some way. That is usually over a USB-A or a USB-C connection to the host.

Many cheap enclosures use USB-C 3.2, which operates at 10 gigabits per second. For a single drive, this is more than enough for a mechanical hard drive to run at full speed, but you may run into issues when using a DAS or a dock with other devices plugged into it.

Thunderbolt is the faster option when it comes to connecting drives to your Mac

Enclosures may also use USB-C 3.2 Gen 2x2, which operates at up to 20 gigabits per second, but if you’re a Mac user, don’t pay more for one. Unfortunately, Apple doesn’t support USB 3.2 Gen 2x2 on Mac, so it will run at the slower 10 gigabits per second.

You can find enclosures that use Thunderbolt or USB 4, which have considerably more bandwidth available. Thunderbolt 3, Thunderbolt 4, and USB 4 run at 40 gigabits per second of bandwidth, which is more than enough for these sorts of drives.

While connection speed is extremely important for an external drive using an SSD or NVMe storage, it’s less essential for mechanical hard drives. It becomes a nice-to-have feature instead.

External hard drive build guide: Recommendations

AppleInsider has looked at quite a few drive enclosures in the past. Here are some recommendations for enclosures that may be the right fit, depending on your data needs.

External hard drive build guide: A standard option - Sabrent 4-Bay

The Sabrent 4-bay DAS is a fairly simple approach to mass local storage, with it having four drive bays and a tray-less hot-swap system. Rather than dealing with RAID, it instead shows each drive as an individual store on your Mac, though you could also rope in your own software RAID configuration.

Sabrent 4-bay DAS

It also connects using a single USB-C cable over USB 3.2 Gen 2, so it connects with up to 10Gbps of bandwidth.

The Sabrent 4-bay DAS is available on Amazon priced at $195.49, without drives.

External hard drive build guide: Thunderbolt 3 enclosure - OWC ThunderBay 4 RAID

A four-bay DAS, the OWC ThunderBay 4 RAID can hold up to 72TB worth of drives, in RAID 0, 1, 4, 5, and 1+0 configurations. You can mix and match hard disks and SSDs, which can result in access speeds of up to 1,572MB/s under sustained loads.

Connecting over Thunderbolt, it has a second Thunderbolt port for daisy-chain usage, and even has a dedicated DisplayPort 1.2 connection.

The OWC ThunderBay 4 RAID is on Amazon priced at $549.99, and from the OWC store, also for $549.99.

External hard drive build guide: Higher-capacity enclosure with speed - OWC ThunderBay 8

Following on from the ThunderBay 4, OWC’s ThunderBay 8 takes the concept but adds more drives. With eight bays that can take a combination of hard drives and SSDs, it has a maximum capacity of 128 terabytes with eight hot-swappable bays.

OWC ThunderBay 8

Again, it has two Thunderbolt 3 ports for daisy-chaining expansion, DisplayPort 1.2 for a 4K screen, and also includes SoftRAID for managing advanced RAID setups.

The OWC ThunderBay 8 is on Amazon, priced at $999.99 without drives, but with combinations including drives also available. It’s also available from OWC for $999.99 in its enclosure-only form, with drive-included packages starting from $1,629.99 with 16TB.

External hard drive build guide: Overkill capacity DAS - TerraMaster D9-320

If you want a lot of drives, check out the TerraMaster D9-320, which we reviewed in October. It’s an enclosure that can handle up to nine drives, which at 24TB per drive equals 216TB in total.

TerraMaster D9-320

You do have to supply your own RAID configuration software, such as SoftRAID for RAID 5 or Disk Utility’s RAID 0 and RAID 1 options. But even so, the sheer capacity is the main feature that consumers will be drawn to here.

The TerraMaster D9-320 is on Amazon priced at $499.99. It’s also available from TerraMaster directly, also at $499.99.

External hard drive build guide: High capacity with ease of use - Sabrent USB 3.2 3.5-inch SATA Hard Drive Tray-less Docking Station

The Sabrent USB 3.2 3.5-inch SATA Hard Drive Tray-less Docking Station is an option if you really need ten drives connected up to your Mac. Capable of taking ten 3.5-inch SATA 6 drives, it does so without needing any fiddling with drive trays or sleds, since you simply slide the drive straight in.

Sabrent USB 3.2 3.5-inch SATA Hard Drive Tray-less Docking Station

Each drive is also set up with independent power switches, so you can hot-swap them if needed. A pair of 120mm fans in the back cool the entire assembly down, while its USB 3.2 Gen2 Type-C connection connects at up to 10Gbps.

Sabrent’s disk tower enclosure is available for $499.99 on Amazon.

External hard drive build guide: Single drive enclosure - Orico Aluminum 3.5 Hard Drive Enclosure with USB 3.2 Gen 2

If you just want to have one drive, there are many cheap enclosures on the market that will hook your hard drive up using USB. One of the more favorable options is the Orico Aluminum Hard Drive Enclosure, which is an aluminum version that connects over both USB-C and USB-A, via an adapter.

Orico Aluminum 3.5 Hard Drive Enclosure with USB 3.2 Gen 2

Capable of taking a 3.5-inch or 2.5-inch drive, it uses aluminum in its casing for heat dissipation. Connecting over USB 3.2 Gen 2, it can use up to 10Gbps of bandwidth, and uses a tool-free design for inserting the drives.

This Orico enclosure is on Amazon, priced at $35.99, but you can find other single-drive enclosures in varying styles and price levels.

External hard drive build guide: Drive Selection

When it comes to the hard drives you put into said enclosures, your choice depends on your specific needs. However, there are two general categories of drive to consider as a home user, rather than anyone needing enterprise-grade support.

For a single-drive enclosure, or for relatively low usage, pretty much any desktop-class consumer hard drive from a major drive producer will work for you.

As an example, the Seagate BarraCuda line starts from 2 terabytes for $64.99, with 8 terabyte drives available from $139.99 on Amazon. Likewise, the WD Blue line includes options for 1 terabyte for $40, 2 terabytes for $65.99, and 12 terabytes for $269.99.

For the multi-drive enclosures, this would be a better fit for drive lines intended for use in a NAS. That includes the Seagate IronWolf lineup, going from $104.99 for 4 terabytes to $219.99 for 12 terabytes, or more if you go for the IronWolf Pro line.

WD Red is Western Digital’s equivalent, starting from $83.97 for 2 terabytes, $249.99 for 10 terabytes.

Our preferred drive that we use for NAS and RAID testing is the 24TB WD Red Pro, which retails for $479.99 on Amazon.