Xbox Series X back-compat loading times: SSDs and HDDs compared

UPDATE: For the authoritative take on Microsoft's new flagship console, Digital Foundry's full Xbox Series X review is now live.

Xbox Series X backwards compatibility is shaping up to be an absolute home run based on our testing so far - yes, every title we've looked at so far seems to hit their performance target when 30fps or 60fps caps are in place, games using dynamic resolution scaling can show clear improvements, while we're looking at anything up to a 2x multiplier in GPU performance in games with unlocked frame-rates. On top of that, there's an image quality bonus too: texture filtering is improved via enforced 16x anisotropic filtering. Loading time improvements are also significantly improved - and that's the focus for this follow-up coverage.

You see, there's one disadvantage to the next-gen dream. Storage space on the internal solid state drive is at a premium - Xbox Series X ships with 802 useable gigs on the 1TB drive. On the one hand, that's actually an improvement over the 781GB of Xbox One X's 1TB HDD (my theory: Microsoft uses its hardware decompression engines to reduce the OS footprint, the console decompressing system files on demand). On the other, with the 1TB plug-in expansion drive priced at £220/$220, fast storage for next-gen titles comes at a price premium.

But maybe there is a better place for your library of OG, Xbox 360 and Xbox One titles. Xbox Series X still allows for standard USB drives to be connected to the console, and there's no reason why you can't buy an off-the-shelf SATA SSD or even a faster NVMe equivalent and copy your back-compat library there. And in theory, there may not be too much of a performance penalty for doing so: older Xbox titles cannot access the low level SSD APIs that truly revolutionise storage performance, so it may well be the case that keeping old games on the new drive is actually a sub-optimal use of the space anyway.

With all of this in mind, I set out on a mission to test the most common storage alternatives. I used an off-the-shelf 5TB Seagate Passport drive to tick off the mechanical HDD option, then paired a Samsung 870 QVO SATA SSD with a Sabrent USB to SATA adapter in order to tick off what I suspected would be the option with the best balance of price vs performance. Rounding off the pack, I took a Samsung PM961 NVMe drive out of storage and brought that into play, connecting it to the Series X via the rather splendid Asus ROG Strix Arion - a USB to NVMe adapter that supports both standard type-A and type-C USB. While the PM961 isn't the fastest drive on the market, it should still saturate the Series X's USB interface.

Xbox Series X: What's The Best SSD Option For Back Compat Xbox Games?

The first order of business in establishing a pecking order in performance terms was to run each drive through some standard read/write tests and here, there can only be one measure: my install of Call of Duty Modern Warfare 2019 currently sits at a remarkable 172.2GB of space and it is surely the hottest candidate generally for migrating away from internal storage. During the transfer process, I noticed that was no uniform read or write rate, but as you can see from the table below, the results are intriguing.

As you might expect, the mechanical hard drive does not fair that well at all, but the difference between the SATA and NVMe units is interesting. In terms of raw write speeds, the NVMe drive is predictably quicker, but more curious is the fact that when it comes to read speeds (where we copied Modern Warfare 2019 back from the external storage to the internal drive), the gap closes significantly.

The NVMe drive is still faster, but not necessarily that much faster bearing in mind that we're transferring across 172.2GB of data, where in context, the difference is vanishingly small. In-game performance will be much more reliant on read speeds, suggesting that excellent loading times may well be within grasp for SATA drives, without the need to spend much more on an NVMe alternative.

I kicked off the game tests by revisiting Final Fantasy 15 - the game that saw Series X absolutely trounce Xbox One X in our first back-compat feature. In terms of setting the stage, these initial results are extraordinary. First of all, I found that loading times could vary a touch from run to run, even on the same drive, but the end result sees that while the internal drive on Xbox Series X is almost always the fastest solid state option, the actual load time advantage up against other SSD solutions is barely noticeable. My results varied from no difference whatsoever to just over two seconds.

However, what's equally clear is that in all cases, using a solid state storage device of any flavour delivers a big, big advantage over sticking to a mechanical hard drive like the 5TB Seagate Passport drive I used for my testing. The difference between SSD and HDD can vary quite dramatically based on content, but suffice to say that I know where I'd rather be playing my back-compat titles.

There is an additional game-changer to factor in, however, for owners of current generation Xbox consoles. It turns out that storage speed is only one part of the speed boost you get to loading times via backwards compatibility - the CPU plays just as big role. To put it into perspective, consider the Hexatheon's Blessings save below. I took the same NVMe drive over to Xbox One X and loaded the same data. What took the Series X console 17.3 seconds to complete balloons to a massive one minute, 12.8 seconds on the older console. Yes, on this game at least, loading on a mechanical drive on Series X is a faster enterprise than using an SSD on Xbox One X but the ideal solution is to leverage both storage and CPU advantages. In my first back-compat report, the CPU boost offered by the new hardware was so vast, it couldn't be quantified in terms of game frame-rates in CPU-bound scenarios. Short of some kind of major disparity in USB throughput, the evidence here suggests that the new console can indeed deliver a 4x improvement to CPU performance - but it takes raw decompression tests to find the extent of the improvement.

Rise of the Tomb Raider is our next port of call and our first test concerns loading up the game from scratch - a test that may have less relevance in the next-gen era. The first time I did so on Xbox Series X, Quick Resume kicked in, taking me back to exactly where I was previously. This is great for gamers, but not so good for loading time analysis and you can purge the Quick Resume state from storage by exiting the application from the console front-end. The end result shows the game booting in nigh-on identical times from any of our storage solutions. There's literally no need to use precious internal SSD space for this one.

What's interesting here is that loading times are fairly decent across the board, and even the mechanical drive fares fairly well - and what I also found fascinating was that taking the Samsung PM961 drive in the Asus enclosure over to Xbox One X saw some fairly close comparisons when it came to level loading. For example, the Lost Expedition level load only took Xbox One X just under three seconds longer to load. It looks like the CPU is more involved on the initial load, however. The 10.6 second result on Series X balloons to 17.5 seconds on One X.

Borderlands 3 next, but there's not much in the way of additional information to impart - once again the solid state storage drives deliver nigh-on identical results whether we're looking at initial loads or indeed level loads. I did test further titles such as Fallout 4 and Just Cause 3, but the story is always the same. It looks to me like storing backwards compatible titles on the internal drive offers minimal advantages, and sometimes no real boost at all. The NVMe drive via USB seems to have a write speed advantage, but this only manifests to any meaningful extent when copying bulk data away from the internal SSD, otherwise you're good to go with SATA.

Once a level loads in Borderlands 3, there is a noticeable degree of texture streaming, where higher quality assets pop into view. Different textures resolve fully at different times. There didn't seem to be any discernible pecking order here between our various solid state storage units, but all of them noticeably outperformed the mechanical hard drive.

One final note: you may have observed that even though we are booting from the SSD, there's still a relatively long period of time to wait from boot to being able to make a selection on the option screen - which further endorses the convenience of Quick Resume. But if 55 seconds sounds like a long time to wait, it's still a night and day improvement over Xbox One X running from the same NVMe drive, where the same process completed in an astonishing two minutes and 21 seconds - enough time to make a sandwich or enjoy a toilet break.

Before reaching a final conclusion, I wanted to share an additional piece of data. To begin with, I benchmarked the Samsung 870 QVO SATA drive using a no-name USB 3.0 to SATA adapter I bought from Amazon. I wasn't entirely sure of the results, so I tested all of the adapters I have in my collection and found that a USB 3.1 bridge cable from Sabrent was the fastest, the extent of its speed boost varying from title to title. As you can see below, just the choice of adapter can have a fairly big impact on loading times, so I'd suggest factoring that into the equation if you're looking to use a loose 2.5-inch SATA drive as the best price vs performance home for your back-compat titles.

Of course, you may be tempted to go for a more robust off-the-shelf solution that integrates both SATA drive and USB adapter into an all-in-one product. This is a great idea, but I would read reviews for the products in question and ensure that you're getting a full USB 3.1/3.2 bandwidth connection between the drive and the source. PC benchmarks from review should do the job just fine here in ascertaining just how much bandwidth you're getting.

Ultimately, I came away pleasantly surprised by the results. The hype surrounding next generation solid state drives has reached a fever pitch, but the bottom line is that it's going to be low level access via the Xbox Velocity Architecture that really sees the SSD reaching its full potential. With the existing library of Xbox games, we're looking at results similar to what we see on PC - an accelerant, and a wonderful one when paired with the huge leap in CPU decompression performance, but what we're seeing here really does suggest that the internal drive or indeed the bespoke £220/$220 external SSD is not really a must for your current library of Xbox games - you'll do just fine with a USB alternative, be it SATA or USB-based in nature.

All of which makes me wonder just how more performance there is to extract from the internal unit via the Xbox Velocity Architecture - and that's something we hope to be able to show you soon as the focus on backwards compatibility with Xbox Series X shifts to titles actually designed with the new console in mind.