It’s common knowledge that Apple doesn’t exactly discount pricing on internal memory or storage options. With Intel Macs, it has been popular to buy as little as essential in a new Mac, and enhance or upgrade them using third-party products. This article considers whether that strategy works when buying an M1 or subsequent Apple Silicon Mac.
First, let me explain what I’ve done in my four current Macs, so you know where I’m coming from. My main production system is an iMac Pro with base specification, which means 32 GB memory, 1 TB internal SSD. As I’m a bit of a hoarder, that has an additional 10 TB of SATA SSDs attached to it. I also have a secondary Intel system, a MacBook Pro 16-inch, which has 16 GB of memory and 500 GB SSD, and is mainly a fallback and for testing laptop-specific issues. My two M1 Macs are similar in specification: a mini with 16 GB of memory and 500 GB SSD, and a MacBook Pro with the same. They’re not normally used in production, but the mini is my mainstay for looking at everything M1.
Selecting memory capacity is the simpler of the two decisions. What you want to aim for is sufficient physical memory to avoid routine use of virtual memory, when you’re going about your normal tasks. Although plenty of utilities offer help in monitoring use of VM or ‘swap’, those in Disk Utility and Activity Monitor are quite good enough for this purpose.
When you’re working normally, with all your mainstay apps busy, open Disk Utility, select the boot Container, and look at how big the VM volume is. If it’s KB, then your Mac hasn’t used any VM since it last started up. Confirm that there’s no “Swap used” in the Memory tab of Activity Monitor too. That should mean that sticking to the same amount of physical memory in your new system performs similarly, and uses VM seldom, if at all. It’s harder to tell whether reducing the amount of real memory will result in significant use of VM, and tricks like creating a large RAM disk can’t accurately simulate the effect of less RAM.
That sets your target for physical memory, aiming to let your new Mac also avoid using VM as much as possible. It won’t work quite the same, because of its Unified Memory, but that should at least get your Mac into the right ballpark.
You have more latitude in choosing the size of its SSD, but here considerations become more complex. Your starting point should be based on your Mac’s current internal storage, complete with your full Home folder.
You may well be able to reduce from that by moving files from your internal SSD to an external disk, which is what I have done with the greater part of my Home folder. Remember that, unless you spend a lot on your external storage, it’s going to be slower to write to and read from than the internal SSD. Where speed becomes more critical – in my case, Xcode projects and their builds – you’ll want to keep those on the internal SSD. But for all those PDFs and other gubbins that we accumulate, an external SATA SSD connected by USB-C is normally quite sufficient.
Be careful over large music, photo and other libraries, though. Most are easy to relocate, but sometimes getting a move to work is painful. Be critical too: if you make movies, you’ll want to do as much of that as possible on your fast internal storage; movies which you merely want to watch can easily go out to cheaper and slower disks.
On the other hand, there are good reasons for ensuring that your internal storage is rather larger than the smallest it needs to be. With HFS+, when pushed, you could fill a disk down to its last few kilobytes before bad things started to happen. You definitely don’t want to do that with internal storage with your boot system on it. I aim to keep an absolute minimum of 200 GB free space on my boot disk. That may seem a lot, but there are moments when that comes under pressure and can fall below 100 GB, which makes be nervous. Ample free space on your boot disk is a wise investment.
There’s another good reason for going for a larger SSD: wear. Conventional wisdom is that the memory used in SSDs has a finite number of times it can be erased, which is a necessary precursor to that block of memory being written to. Thus, the life of your Mac’s SSD may well be determined by the total amount of data written to it divided by its total capacity. Avoiding the use of VM will significantly reduce the amount of data written to it, and using a larger SSD obviously increases its capacity, hence should prolong its life. The worst option is to have a small SSD which is heavily used for VM. In worst cases, that can wear SSDs out in a couple of years rather than ten or more.
You can then balance your equation: how much smaller your SSD can be by moving less active files to external storage, and how much larger it needs to be to avoid running short of free space, and controlling wear.
There’s one final consideration which you need to temper this with: performance. Apple’s internal SSDs are blisteringly quick by any test. If you need to match that performance, particularly when writing files, on an external SSD, it’s going to be expensive.
When we think of the cost of SSDs, we tend to think in terms of SATA models working over USB-C connections, which are quite cheap until you get up to large sizes. On a good day, they’ll return performance around a fifth or sixth that of an internal SSD, and that is noticeable. To get performance comparable with an internal SSD, you have to move up to M.2 with NVMe running through a Thunderbolt 3 interface.
Unfortunately, although quite expensive enough already, M.2 SSDs have a serious shortcoming: they get hot, particularly when performing continuous writing, a function which is usually one of the reasons for paying extra for their speed. Compact M.2 SSDs can almost invariably be pushed into thermal throttling during write testing, it’s just a matter of time and a warm office environment. That’s because they rely on passive cooling.
The solution should be simple: a powered enclosure with a cooling fan and air vents, and plenty of space around each SSD stick. Finding one to accommodate M.2 modules isn’t easy, nor are they cheap. Add the cost of one of these fan-cooled enclosures to that of your M.2 sticks, and you’ll discover that Apple’s SSD pricing isn’t so bad after all. Then there’s the limitation on using NVMe lanes – only 1 per stick, I gather – which means that the only way you can match the performance of the internal SSD is to run an external M.2 RAID. By the end of all this, you’ll probably have paid more for your external storage, or you’ll have something which is noticeably inferior.
Apple’s SSDs aren’t cheap, but they’re a great deal less hassle, and deliver consistently high performance in Macs with active cooling systems. If that’s what you need, then there’s no better deal, not for the moment, at least. My next Apple Silicon Mac is going to have the maximum amount of memory, and at the very least a 1 TB internal SSD. It’ll be cheaper in the long run.