Storage Matters: Why Xbox and Playstation SSDs Usher In A New Era of Gamingby Billy Tallis on June 12, 2020 9:30 AM EST
- Posted in
- Xbox Series X
- PlayStation 5
A new generation of gaming consoles is due to hit the market later this year, and the hype cycle for the Xbox Series X and Playstation 5 has been underway for more than a year. Solid technical details (as opposed to mere rumors) have been slower to arrive, and we still know much less about the consoles than we typically know about PC platforms and components during the post-announcement, pre-availability phase. We have some top-line performance numbers and general architectural information from Microsoft and Sony, but not quite a full spec sheet.
The new generation of consoles will bring big increases in CPU and GPU capabilities, but we get that with every new generation and it's no surprise when console chips get the same microarchitecture updates as the AMD CPUs and GPUs they're derived from. What's more special with this generation is the change to storage: the consoles are following in the footsteps of the PC market by switching from mechanical hard drives to solid state storage, but also going a step beyond the PC market to get the most benefit out of solid state storage.
Solid State Drives were revolutionary for the PC market, providing immense improvements to overall system responsiveness. Games benefited mostly in the form of faster installation and level load times, but fast storage also helped reduce stalls and stuttering when a game needs to load data on the fly. In recent years, NVMe SSDs have provided speeds that are on paper several times faster than what is possible with SATA SSDs, but for gamers the benefits have been muted at best. Conventional wisdom holds that there are two main causes to suspect for this disappointment: First, almost all games and game engines are still designed to be playable off hard drives because current consoles and many low-end PCs lack SSDs. Game programmers cannot take full advantage of NVMe SSD performance without making their games unplayably slow on hard drives. Second, SATA SSDs are already fast enough to shift the bottleneck elsewhere in the system, often in the form of data decompression. Something aside from the SSD needs to be sped up before games can properly benefit from NVMe performance.
Microsoft and Sony are addressing both of those issues with their upcoming consoles. Game developers will soon be free to assume that users will have fast storage, both on consoles and on PCs. In addition, the new generation of consoles will add extra hardware features to address bottlenecks that would be present if they were merely mid-range gaming PCs equipped with cutting-edge SSDs. However, we're still dealing with powerful hype operations promoting these upcoming devices. Both companies are guilty of exaggerating or oversimplifying in their attempts to extol the new capabilities of their next consoles, especially with regards to the new SSDs. And since these consoles are still closed platforms that aren't even on the market yet, some of the most interesting technical details are still being kept secret.
The main source of official technical information about the PS5 (and especially its SSD) is lead designer Mark Cerny. In March, he gave an hour-long technical presentation about the PS5 and spent over a third of it focusing on storage. Less officially, Sony has filed several patents that apparently pertain to the PS5, including one that lines up well with what's been confirmed about the PS5's storage technology. That patent discloses numerous ideas Sony explored in the development of the PS5, and many of them are likely implemented in the final design.
Microsoft has taken the approach of more or less dribbling out technical details through sporadic blog posts and interviews, especially with DigitalFoundry (who also have good coverage of the PS5). They've introduced brand names for many of their storage-related technologies (eg. "Xbox Velocity Architecture"), but in too many cases we don't really know anything about a feature other than its name.
Aside from official sources, we also have leaks, comments and rumors of varying quality, from partners and other industry sources. These have definitely helped fuel the hype, but with regards to the console SSDs in particular, these non-official sources have produced very little in the way of real technical details. That leaves us with a lot of gaps that require analysis of what's possible and probable for the upcoming consoles to include.
What do we know about the console SSDs?
Microsoft and Sony are each using custom NVMe SSDs for their consoles, albeit with different definitions of "custom". Sony's solution aims for more than twice the performance of Microsoft's solution and is definitely more costly even though it will have the lower capacity. Broadly speaking, Sony's SSD will offer similar performance to the high-end PCIe 4.0 NVMe SSDs we expect to see on the retail market by the end of the year, while Microsoft's SSD is more comparable to entry-level NVMe drives. Both are a huge step forward from mechanical hard drives or even SATA SSDs.
|Console SSD Confirmed Specifications|
Xbox Series X
|Capacity||1 TB||825 GB|
|Speed (Sequential Read)||2.4 GB/s||5.5 GB/s|
|Host Interface||NVMe||PCIe 4.0 x4 NVMe|
The most important and impressive performance metric for the console SSDs is their sequential read speed. SSD write speed is almost completely irrelevant to video game performance, and even when games perform random reads it will usually be for larger chunks of data than the 4kB blocks that SSD random IO performance ratings are normally based upon. Microsoft's 2.4GB/s read speed is 10–20 times faster than what a mechanical hard drive can deliver, but falls well short of the current standards for high-end consumer SSDs which can saturate a PCIe 3.0 x4 interface with at least 3.5GB/s read speeds. Sony's 5.5GB/s read speed is slightly faster than currently-available PCIe 4.0 SSDs based on the Phison E16 controller, but everyone competing in the high-end consumer SSD market has more advanced solutions on the way. By the time it ships, the PS5 SSD's read performance will be unremarkable – matched by other high-end SSDs – except in the context of consoles and low-cost gaming PCs that usually don't have room in the budget for high-end storage.
Sony has disclosed that their SSD uses a custom controller with a 12-channel interface to the NAND flash memory. This seems to be the most important way in which their design differs from typical consumer SSDs. High-end consumer SSDs generally use 8-channel controllers and low-end drives often use 4 channels. Higher channel counts are more common for server SSDs, especially those that need to support extreme capacities; 16-channel controllers are common and 12 or 18 channel designs are not unheard of. Sony's use of a higher channel count than any recent consumer SSD means their SSD controller will be uncommonly large and expensive, but on the other hand they don't need as much performance from each channel in order to reach their 5.5GB/s goal. They could use any 64-layer or newer TLC NAND and have adequate performance, while consumer SSDs hoping to offer this level of performance or more with 8-channel controllers need to be paired with newer, faster NAND flash.
The 12-channel controller also leads to unusual total capacities. A console SSD doesn't need any more overprovisioning than typical consumer SSDs, so 50% more channels should translate to about 50% more usable capacity. The PS5 will ship with "825 GB" of SSD space, which means we should see each of the 12 channels equipped with 64GiB of raw NAND, organized as either one 512Gbit (64GB) die or two 256Gbit (32GB) dies per channel. That means the nominal raw capacity of the NAND is 768GiB or about 824.6 (decimal) GB. The usable capacity after accounting for the requisite spare area reserved by the drive is probably going to be more in line with what would be branded as 750 GB by a drive manufacturer, so Sony's 825GB is overstating things by about 10% more than normal for the storage industry. It's something that may make a few lawyers salivate.
It's probably worth mentioning here that it is unrealistic for Sony to have designed their own high-performance NVMe SSD controller, just like they can't do a CPU or GPU design on their own. Sony had to partner with an existing SSD controller vendor and commission a custom controller, probably assembled largely from pre-existing and proven IP, but we don't know who that partner is.
Microsoft's SSD won't be pushing performance at all beyond normal new PC levels now that OEMs have moved beyond SATA SSDs, but a full 1TB in a PC priced similarly to consoles would still be a big win for consumers. Multiple sources indicate that Microsoft is using an off-the-shelf SSD controller from one of the usual suspects (probably the Phison E19T controller), and the drive itself is built by a major SSD OEM. However, they can still lay claim to using a custom form factor and probably custom firmware.
Neither console vendor has shared official information about the internals of their SSD aside from Sony's 12-channel specification, but the capacities and performance numbers give us a clue about what to expect. Sony's pretty much committed to using TLC NAND, but Microsoft's lower performance target is down in the territory where QLC NAND is an option: 2.4GB/s is a bit more than we see from current 4-channel QLC drives like the Intel 665p (about 2GB/s) but much less than 8-channel QLC drives like the Sabrent Rocket Q (rated 3.2GB/s for the 1TB model). The best fit for Microsoft's expected performance among current SSD designs would be a 4-channel drive with TLC NAND, but newer 4-channel controllers like the Phison E19T should be able to hit those speeds with the right QLC NAND. Either console could conceivably in the future get a double-capacity version that uses QLC NAND to reach the same read performance of the original models.
DRAMless, but that's OK?
Without performance specs for writes or random reads, we cannot rule out the possibility of either console SSD using a DRAMless controller. Including a full-sized DRAM cache for the flash translation layer (FTL) tables on a SSD primarily helps performance in two ways: better sustained write speeds when the drive's full enough to require a lot of background work shuffling data around, and better random access speed when reading data across the full range of the drive. Neither of those really fits the console use case: very heavily read-oriented, and only accessing one game's dataset at a time. Even if game install sizes end up being in the 100-200GB range, at any given moment the amount of data used by a game won't be more than low tens of GB, and that is easily handled by DRAMless SSDs with a decent amount of SRAM on the controller itself. Going DRAMless seems very likely for Microsoft's SSD, and while it would be very strange in any other context to see a 12-channel DRAMless controller, that option does seem to be viable for Sony (and would offset the cost of the high channel count).
The Sony patent mentioned earlier goes in depth on how to make a DRAMless controller even more suitable for console use cases. Rather than caching a portion of the FTL's logical-to-physical address mapping table in on-controller SRAM, Sony proposes making the table itself small enough to fit in a small SRAM buffer. Mainstream SSDs have a ratio of 1 GB of DRAM for each 1 TB of flash memory. That ratio is a direct consequence of the FTL managing flash in 4kB chunks. Having the FTL manage flash in larger chunks directly reduces the memory requirements for the mapping table. The downside is that small writes will cause much more write amplification and be much slower. Western Digital sells a specialized enterprise SSD that uses 32kB chunks for its FTL rather than 4kB, and as a result it only needs an eighth the amount of DRAM. That drive's random write performance is poor, but the read performance is still competitive. Sony's patent proposes going way beyond 32kB chunks to using 128MB chunks for the FTL, shrinking the mapping table to mere kilobytes. That requires the host system to be very careful about when and where it writes data, but the read performance that gaming relies upon is not compromised.
In short, while the Sony SSD should be very fast for its intended purpose, I'm going to wager that you really wouldn't want it in your Windows PC. The same is probably true to some extent of Microsoft's SSD, depending on their firmware tuning decisions.
Both Microsoft and Sony are providing expandability for the NVMe storage of their upcoming consoles. Microsoft's solution is to re-package their internal SSD into a custom removable form factor reminiscent of what consoles used back when memory cards were measured in MB instead of TB and before USB flash drives were ubiquitous. Since it uses all the same components, this expansion card will be functionally identical to the internal storage. The downside is that Microsoft will control the supply and probably pricing of the cards; currently Seagate is the only confirmed partner for selling these proprietary expansion cards.
Sony is taking the opposite approach, by giving users access to a standard M.2 PCIe 4.0 slot that can accept aftermarket upgrades. The requirements aren't entirely clear: Sony will be doing compatibility testing with third-party drives in order to publish a compatibility list, but they haven't said whether drives not on their approved list will be rejected by the PS5 console. To make it onto Sony's compatibility list, a drive will need to mechanically fit (ie. no excessively large heatsink) and offer at least as much performance as Sony's custom internal SSD. The performance requirements mean no drive currently available at retail will qualify, but the situation will be very different next year.
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almighty15 - Sunday, June 14, 2020 - linkIt should read "By the time it ships, the PS5 SSD's read performance will be unremarkable – matched by other high-end SSDs ON PAPER"
In terms of real world performance a 5Gb/s NVMe drive can't beat a 550Mb/s SATA III SSD and yet Anandtech somehow think they'll compete with console?
Eliadbu - Saturday, June 13, 2020 - linkThis change might in few years make games to require SSD at certain speed as a base requirement. I'm for it since I feel my NVME SSDs are not helpful in gaming more than my SATA ssd. In many cases you need the consoles to make a move for PCs to enjoy it, I see this as definitely a case of such.
vol.2 - Saturday, June 13, 2020 - linkSo, is the PS5 officially the ugliest console ever created?
wrkingclass_hero - Sunday, June 14, 2020 - linkIt's up there.
wolfesteinabhi - Saturday, June 13, 2020 - linkwith main cpu/gpu being very identical in both camps they are running out of ways to differentiate.
storage is important though .. but i wish they woukd stick to some common standard ....and over time we get games that can be played on either of the consoles or they can be htpcs in itself that can do a lot more from their h/w than just games .... given current hardware they have ... i feel its a bit wasted when they are only limited to games(that too a very limited amlunt..especially Sony/PS)
almighty15 - Sunday, June 14, 2020 - linkI don't normally comment on article like this but feel I have due to the tone you have regarding PC 'catching up' to consoles.
That is a long way away, I'm talking years! As I explained on Twitter a 5Gb/s NVMe drives loads games no faster then a 550Mb/s SATA III SSD, and while some of that is down to having to cater to machines that still run mechanical drives most of it is due to Windows just having a file and I/O systems that decades old.
If we want to send a texture to a GPU on PC this is the 'hardware' path it has to take:
SSD > system bus > Chipset (South bridge) > system bus > CPU > system bus > main RAM >
system bus > CPU (North bridge) > PCIEX bus > VRAM
To get a texture to GPU memory on PlayStation 5 it goes:
SSD > system bus > I/O controller > system bus > VRAM
On PC these system buses and chips all run and communicate with each other at different speeds which causes bottlenecks as data is moved through all that hardware.
On PS5 the path is so much straight forward and the I/O block runs at the same speed as the CPU clock so it's all super faster and efficient.
And then on PC there's the software side of it, which again is a HUGE problem that Microsoft can't fix with a little Windows update. The hardware on PC can not directly talk to other hardware, meaning your GPU can not directly talk to the storage driver and ask it for a texture, it has to ask Windows, who then ask the chipset driver, who then asks the storage driver for a file.......
It requires a complete RE-WRITE of Windows storage drivers and kernal which is a process that takes years as they have to send any new idea's over to developers and software owners so they can do their own testing and plan patching their existing software.
When Apple updated their file system for SSD it them 3 years! And they way less legacy hardware and hardware configurations to worry about then Micorosft.
There is currently nothing in the develop changes about a new version of Windows or a new file system in the works meaning that it's at least 3-4 years away.
This article doesn't even scratch the surface as to why storage and I/O is so slow and bottlenecked on PC and make it out to be like it's a simple fix to get PC SSD's performing like consoles.
PC's will catch up, they always do, but do not let articles like this one trick you in to thinking it's a quick fix as it most certainly isn't.
eddman - Sunday, June 14, 2020 - linkAs mentioned in this very article, they have this new DirectStorage API on XSX and plan to bring it to windows. They haven't released any specific details but it might even be some sort of a direct GPU/VRAM-to-storage solution.
Whatever it is, it's surely bound to improve the file transfer performance, and since it'd be part of the Directx suite, developers should have an easy time taking advantage of it.
Billy Tallis - Sunday, June 14, 2020 - linkYour description of how the data paths differ between a standard PC and the PS5 is wildly inaccurate.
eddman - Sunday, June 14, 2020 - linkYea, the path is wrong. For one, RAM is not connected to the CPU through the system bus. It's something like this for desktops, IINM:
1. Intel/Ryzen (SSD connected to the chipset):
SSD > PCIe > Chipset > system bus (DMI/PCIe x4) > CPU > memory channel > RAM > memory channel > CPU(*) > PCIe x16 > VRAM
2. Ryzen (SSD connected directly to the CPU):
SSD > PCIe > CPU > memory channel > RAM > memory channel > CPU(*) > PCIe x16 > VRAM
(*) at this step, perhaps the CPU has already done the I/O calculations, so the data goes directly from the system RAM (through the memory controller and then PCIe x16) to the VRAM (without wasting CPU cycles)?
(I don't know that much about hardware at such low levels, so please correct me if I'm wrong.)
With a GPU-to-storage direct access, it should look like these:
1. SSD > PCIe > Chipset > system bus (DMI/PCIe x4) > CPU(!) > PCIe x16 > VRAM
2. SSD > PCIe > CPU(!) > PCIe x16 > VRAM
The second option doesn't look much different from the PS5.
(!) just passing through CPU's System Agent/Infinity Fabric with minimal CPU overhead.
Billy Tallis - Sunday, June 14, 2020 - linkIt is important to make a distinction between when data hits the CPU die but doesn't actually require attention from a CPU core. DMA is important! Data coming in from the SSD can be forwarded to RAM or to the GPU (P2P DMA) by the PCIe root complex without involvement from a CPU core. The CPU just needs to initiate the transaction and handle the completion interrupt (which often involves setting up the next DMA transfer).
On the PS5, there will also be a DMA round-trip from RAM to the decompression unit back to RAM, with either a CPU core or the IO coprocessor setting up the DMA transfers.