Slashdot Mirror
New PCIe SSDs Load Games, Apps As Fast As Old SATA Drives
crookedvulture writes Slashdot has covered a bunch of new PCI Express SSDs over the past month, and for good reason. The latest crop offers much higher sequential and random I/O rates than predecessors based on old-school Serial ATA interfaces. They're also compatible with new protocols, like NVM Express, which reduce overhead and improve scaling under demanding loads. As one might expect, these new PCIe drives destroy the competition in targeted benchmarks, hitting top speeds several times faster than even the best SATA SSDs can muster. The thing is, PCIe SSDs don't load games or common application data any faster than current incumbents—or even consumer-grade SSDs from five years ago. That's very different from the initial transition from mechanical to solid-state storage, where load times improved noticeably for just about everything. Servers and workstations can no doubt take advantage of the extra oomph that PCIe SSDs provide, but desktop users may struggle to find scenarios where PCIe SSDs offer palpable performance improvements over even budget-oriented SATA drives.
A PCIe SSD opens up the sole SATA slot for the backup disk in the small form factor PCs that are currently in vogue.
I should use this sig to advertise my book ISBN-13 : 978-1501515132.
Since so many games make you sit through crappy videos, copyright screens and other garbage for thirty seconds while they start up, or at least make you hit a key or press a mouse button to skip them and that damn 'Press Any Key To Start' screen that they couldn't even take five minutes to remove when porting from a console, faster load time is pointless once you've eliminated the worst HDD delays.
A guy named Amdahl had something to say on the subject. SSDs excel at IOPS, but that buys you little if you're not IOPS-constrained.
Examples of things that eat operations as fast as you can throw them at 'em: databases, compilation, most server daemons.
Examples of things that couldn't care less: streaming large assets that are decompressed in realtime, like audio or video files. Loading a word processing document. Downloading a game patch. Encoding a DVD. Playing RAM-resident video games.
It should be a shock to roughly no one that buffing an underused part won't make the whole system faster. I couldn't mow my lawn any faster if the push mower had a big block V8, nor would overclocking my laptop make it show movies any faster.
TL;DR non-IO-bound things don't benefit from more IO.
Dewey, what part of this looks like authorities should be involved?
That's just it. Their speeds are not "much higher." They're only slightly faster. The speed increase is mostly an illusion created by measuring these things in MB/s. Our perception of disk speed is not MB/s, which is what you'd want to use if you only had x seconds of computing time and wanted to know how many MB of data you could read.
Our perception of disk speed is wait time, or sec/MB. If I have y MB of data I need read, how many seconds will it take? This is the inverse of MB/s. Consequently, the bigger MB/s figures actually represent progressively smaller reductions in wait times. I posted the explanation a few months ago, the same one I post to multiple tech sites. And oddly enough Slashdot was the only site where it was ridiculed.
If you measure these disks in terms of wait time to read 1 GB, and define the change in wait time from a 100 MB/s HDD to a 2 GB/s NVMe SSD as 100%, then:
A 100 MB/s HDD has a 10 sec wait time.
A 250 MB/s SATA2 SSD gives you 63% of the reduction in wait time (6 sec).
A 500 MB/s SATA3 SSD gives you 84% of the reduction in wait time (8 sec).
A 1 GB/s PCIe SSD gives you 95% of the reduction in wait time (9 sec).
The 2 GB/s NVMe SSD gives you 100% of the reduction in wait time (9.5 sec).
Or put another way:
The first 150 MB/s speedup results in a 6 sec reduction in wait time.
The next 250 MB/s speedup results in an extra 2 sec reduction in wait time.
The next 500 MB/s speedup results in an extra 1 sec reduction in wait time.
The next 1000 MB/s speedup results in an extra 0.5 sec reduction in wait time.
Each doubling of MB/s results in half the reduction in wait time of the previous step. Manufacturers love waving around huge MB/s figures, but the bigger those numbers get the less difference it makes in terms of wait times.
(The same problem crops up with car gas mileage. MPG is the inverse of fuel consumption. So those high MPG vehicles like the Prius actually make very little difference despite the impressively large MPG figures. Most of the rest of the world measures fuel economy in liters/100 km for this reason. If we weren't so misguidedly obsessed with achieving high MPG, we'd be correctly attempting to reduce fuel consumption by making changes where it matters the most - by first improving the efficiency of low-MPG vehicles like trucks and SUVs even though this results in tiny improvements in MPG.)