Is your Mac's hard drive near capacity, full to the brim with music, photos and videos? Do you have a Mac with a small SSD drive, having sacrificed storage space for the extra speed offered by flash storage? Are you confronted with having to delete photos and other media in order to accommodate your ever increasing photo library? If so then it may be time to add more storage.

Modern Macs don't allow you to upgrade the internal storage after purchase, so your options include various external solutions. There are plenty to choose from, ranging from a desktop hard drive or a network attached storage device, to a portable flash drive (often referred to as an SSD, or solid state drive), and even cloud storage that you can access via the internet.

There are also a variety of ways to connect your external drive to your Mac. You will face a choice of USB, FireWire and Thunderbolt, plus you can connect to storage via WiFi, or via the internet.

So how do you decide what kind of storage is best for you?

Read our round up of the best storage devices available now: Best storage options for Mac

What sort of storage should I get to go with my Mac?

You need to start by answering a few questions. Do you want to be able to take your storage with you? Do you want to be able to access your data anywhere in the world? Do you want the maximum amount of storage available? Do you want to be able to back up your data as quickly as possible? Or, do you want the cheapest storage solution you can get?

Different people need different things from their external storage. If you are only going to copy a few files at a time onto your storage device speed may not be important, but if you are likely to be copying over gigabytes of data in a hurry, speed will be high on your wish list. Similarly, we may recommend a NAS drive, but if all you want is a small drive you can pop in your bag then it's not going to be the best choice for you. Keep your requirements in mind as you read the following.

Should I get a flash (SSD) drive or a hard drive?

Read more: Best SSD for Mac | Best Mac hard drives

SPEED: If speed is what is important to your then an SSD drive could be a good option. SSD drives can access data much faster because there are no mechanical components and data is accessed electronically. A hard disk drive (HDD) on the other hand will take more time because the data is accessed electromechanically.

This is why Macs that feature an SSD drive inside are a lot faster than Macs that sport hard drives. A MacBook with an SSD will start up in a matter of seconds.

Just to add to the variety, among hard drives there can be differences in speed. Some drives will offer a rotational speed of 7200 rpm, while other drives spin at 5400 rpm.  Pro users who do professional-level audio or video production might consider a 10,000- to 15,000-rpm drive, for optimal performance, but these high-performance drives usually offer less storage capacity and require a SCSI connection.

RELIABILITY: The other reason why SSDs are considered superior to hard disks is the fact that an SSD has no moving parts. This means no mechanics to break, even when a machine is jostled or dropped. An HDD is more likely to suffer from mechanical failure or physical damage because of the moving parts. However, reports also suggest that an SSD's performance may degrade over time and if it does you are likely to completely lose your data. Traditional hard drives, on the other hand will tend to warn you of the impending failure and the recovery of data may be possible.

PORTABILITY: If you are going to be carrying the drive around with you this is another reason to opt for flash storage. If you carry a hard drive between work and home you are likely to find that one day it fails. There are some hard drives that are designed to be portable, but it is inevitable that due to the mechanical nature of the device one day you will knock it, or drop it, and it will stop working.  The Western Digital My Passport Slim is the most compact of all WD’s Passport range, measuring just 12.3mm thick, 80mm wide and 110mm long. It only weighs 134g too, so you can slip it into a bag or a jacket pocket and carry it around with no trouble at all. It costs £120 for 1TB storage. For extra protection against bumps and wear and tear there's the LaCie Rugged USB 3.0 Thunderbolt Series, which features an orange rubber bumper. There are of course other (newer) SSDs out there which you can find.

NOISE: Because SSD drives do not have a spinning platter they are also completely silent in operation. The noise produced by a hard disk drive may be an issue if you intend to house it somewhere where the audible noise needs to be kept to a minimum. Perhaps your work involves audio, or perhaps you want the storage device to be used in the living room and the noise of it buzzing away in the background would be detrimental to your enjoyment of the films or music stored on it.

CAPACITY: The major benefit of hard disk drives is that they offer more gigabytes of storage for your money. For example you can get around 1TB of storage for less than £80 if you purchase a hard disk drive, it you were looking for 1TB of external flash storage you could be looking at paying at least triple that. (Integral's 1TB USB 3.0 Portable Solid State Drive). Most of the flash options when it comes to external hard drives are USB memory sticks. The capacities have increased and prices have fallen over the past year, so you can now pick up a 128GB USB 3.0 flash drive for £49.99 (Integral Courier 128GB USB 3.0 Flash Drive), but at that price don't expect the read and write speeds of a more expensive offering.  A better option is the PNY StorEDGE 128GB which is actually an SD card, but thanks to the fact that every Mac comes with an SD card reader on the side, you can use it as additional storage. It costs £80. However, we love the Axtremex Micro SSD, 32GB for £130. It's a tiny, portable flash-based drive.

Should I get a portable drive or a desktop drive?

PRICE: As we mentioned above, if you are going to be carrying the drive around with you this is another reason to opt for flash storage. If you only need a few GB of storage then a 16GB flash drive may be ideal for your needs. However, there are some hard drives that are designed to be portable, and they will be a lot cheaper than a flash drive offering any significant amount of storage.

So if price is important then a cheaper portable drive may be the best choice for you. However, a similar capacity desktop hard drive is likely to offer you even more GB for your money than a portable drive will.

RELIABILITY: A portable drive has been designed to withstand knocks and movement, unlike a desktop hard drive. If you attempt to carry a desktop hard drive around you may damage it.

PORTABILITY: Expect a desktop hard drive to be significantly heavier and bulkier than a portable hard drive. Flash or solid state drives will usually be a lot smaller than a portable hard drive, some flash drives are thumb size, others credit card sized. Portable drives have added shock protection for portability.

STYLE: If you are going to buy a hard disk to sit on your desk it might as well look stylish. You can rely on LaCie to add the glamour to the hard drive market, using big-name designers such as Philippe Starck or the Porsche Design studio to come up with visually arresting designs. Their LaCie Blade Runner has an eye-catching design and is priced at £264.99 with 4TB storage.

Should I get a FireWire, USB, Thunderbolt or a WiFi hard drive?

USB is the most common interface for Macs and PCs, and USB 3.0 delivers a faster data rate than USB 2.0 (5 gbps versus 480 mbps) and more electrical power to an attached device (900mA versus 500mA). The newer standard is backward-compatible, so your computer will be able to use a USB 3.0 drive even if the computer has only USB 2.0 ports.

THUNDERBOLT ports are twice as fast as USB 3.0 ports, achieving a raw data transfer rate of 10 gbps. That’s speedy enough to transfer a full-length, high-definition movie in less than 30 seconds. Thunderbolt hard drives are relatively expensive, however. The LaCie Little Big Disk was one of the first available Thunderbolt devices after the technology launched almost three years ago in February 2011, and now this miniature desktop drive has had a boost again in performance. You can get a 1TB SSD drive for £919.

FIREWIRE (also known as IEEE 1394) is another high-speed interface. The FireWire 400 interface can support a data transfer rate of 400 mbps, while the newer FireWire 800 interface can deliver throughput of 786 mbps.

USB, Thunderbolt, and FireWire all provide enough electrical power to run an attached drive, so the only cord you’ll need to carry with you is the appropriate interface cable.

WI-FI OR NETWORK ATTACHED STORAGE (NAS) is storage connected to your network and running specialized software. These solutions often include more than one hard drive, with your data mirrored across the two. This means that if one fails your files are safe. However, there are consumer-oriented network drives now that basically offer users the opportunity to back up and store files without having to plug in the device. This is especially handy if you have a laptop that generally sits on your lap, rather than on a desk beside a hard drive. For example, the WD My Cloud is a NAS drive aims to provide simple remote access of your data, from any internet connection. The 2TB version costs £120. Alternatively, there's the Synology DiskStation DS214, a two-bay NAS enclosure, which means it ships without disks. It supports up to 8TB of storage with a pair of 4TB drives that you can add yourself (which may save you some money). The enclosure costs £216 ex VAT.

A NAS drive will allow you to back your Mac up using Time Machine regularly, something you may be less likely to do if you have to plug your Mac into a drive from time to time. (Read more: Best NAS for Mac.)

RAID: Some desktop external hard drives have more than one hard drive inside. With two drives, the unit can be configured as a striped array (called RAID 0), which makes one partition of the two drives and writes and reads simultaneously for faster performance. If one of the drives dies, you lose all of your data. The two drives can also be configured as a mirrored array (called RAID 1). Mirroring the drives safeguards your data by keeping two identical copies of your drive. The downside is that you can only use half of the unit’s storage capacity. Some two-drive external devices can also be configured to use the drives individually in a JBOD (Just a Bunch of Disks) setup. This way both drives mount separately as if they were two one-disk external drives. If one drive dies, the other can continue to operate. 

The G-Technology G-RAID mini contains two 1TB drives and costs about £350.00. The drive comes formatted for use with Macs, and in the RAID 0 format, which provides maximum performance by ‘striping’ your data across the two drives.

THE CLOUD: Another solution might be to rent storage space in the cloud, but buying a hard-drive’s worth of capacity is prohibitively expensive: for example, 1000GB of storage on Dropbox, will set you back £79 per year. Buying a portable hard drive is far more economical.

In comparison you can pick up a 2TB drive for a fraction of the price.

There are cheaper or free cloud options, of course. You can get 2GB free space on DropBox. But it's likely that 2GB won't stretch very far if you are looking for somewhere to back up files.

SPEED: As you can see, there are a number of interfaces to choose from and your choice depends on the Mac you own. The majority of new Macs offer Thunderbolt, but at the moment this is quite an expensive option. However, transfer speeds are far faster, with Apple claiming Thunderbolt transfer speeds of up to 10Gbits/sec. In contrast, USB 3.0 offers around 5Gbits/sec. USB 2.0 on the other hand offers only 380 Mbit/sec, so if your Mac is very old and only offers USB 2.0 transfer speeds will be slow. If you find a cheap USB 2.0 hard drive you will be able to plug into a USB 3.0 port on your Mac, but speeds will be no faster.

PRICE: As we mention above Thunderbolt is quite an expensive option. A WD My Book Thunderbolt Duo with 4TB storage is £439.99, while the WD My Book Studio with USB 3 and 4TB storage costs £179. You could alternatively opt for a network attached hard drive such as the My Book Live Duo that will connect to your Mac via Gigabit Ethernet.  You will also be able to access this drive via your iPad and iPhone. A 4TB My Book Live Duo costs £279.30.

How do I know if the drive is compatible with my Mac?

HFS or NTFS? OS X and Windows use different file systems (HFS+ and NTFS, respectively), so most hard-drive manufacturers offer platform-specific models; the drives are pre-formatted accordingly, and the bundled software (if any) is compatible with the given platform. OS X can read files on an NTFS drive, but it can’t write them. If you intend to use the same drive on both platforms, you can install software on your Mac that will enable it to do both: NTFS-3G is a free option.

TIME MACHINE? Almost all USB or FireWire external hard drives are compatible with Time Machine, as long as the drive is HFS+ formatted.

Can I get storage for my iPad/iPhone

There are a number of external storage options that can also be used by your iPad or iPhone. For example, Kingston's Wi-Drive is a small flash drive that you can load files onto via your Mac. When you’re done copying files to the Wi-Drive, you can access the files on the drive on your iPad or iPhone via the Wi-Drive app using Wi-Fi. Once you are connected to the Wi-Drive you can stream movies and music wirelessly. Read more: Best external storage for iPhones and iPads.