What to look for in a performance SSD

The Register has a nice writeup on performance SSDs. The only problem is that performance is really a matter of diminishing returns, and The Reg didn’t report on random I/O.

The problem we run into is that modern SSDs under the best circumstances can saturate the SATA bus. The memory cells may be able to deliver a gigabyte or even a gigabyte and a half of data per second, but the bus can only handle 550 megabytes,

But most I/O isn’t sequential–it’s random. And random I/O even on the fastest drives runs at a rate of below 300 megabytes per second, which is well within what SATA can handle.

So if you pay a hefty premium for a PCIe-connected SSD, you may not be getting much more performance. The system will suspend and resume faster–potentially three times faster–but most everyday work won’t yield much benefit. A Ferrari will lap my Honda Civic on a race track, but when we’re driving in rush hour traffic, the difference in the speed of the two cars will be marginal.

So while the fastest SSD on the market may seem impressive, there’s a much smaller difference between it and a budget SSD than there is between the budget SSD and even the fastest platter drive. So as tempting as it seems to buy a Z97 motherboard and an M.2 SSD, I think I’ll stick with my lower-midrange motherboards and low-tier SSDs. I get a lot more performance per dollar that way, and for anything other than 3D gaming or cryptocurrency mining or password cracking, you won’t notice much difference between one of my $500 systems and a best-of-everything system that costs 10 times as much. And even for those three tasks, I could drop in a better video card to make up the difference if I were interested in such things.

Once I find a performance SSD that can deliver random I/O, particularly writes, at a rate higher than 550 MB/second, I’ll be early in line to buy one. But that’s still probably a couple of years off, at least.

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