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Comment by throwaway7767 | Hacker News Reader

FTA: > The 1TB card is certain to be prohibitively expensive, and at such a large capacity, read and write speeds are going to be comparatively slow

Why would a larger card be slower? Wouldn't it be faster since it can write more flash cells in parallel? Larger SSDs are usually a bit faster due to this.

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Another poster referred to this, but the most obvious reason for slow speed is intentional throttling due to thermal concerns.

It might actually have to be simply capped at an "always-safe" write speed due to limitations on the circuitry - is there room in an SD card format for adequate thermal sensors and the logic to limit write speed as the card heats up?

Oh god, we're talking about overclocking SD cards? I can't wait to see experimental results not only in general, but also in edge case scenarios like when encountering counterfeit hardware.

Discussion doesn't seem to be really widespread, but particularly with the M.2 / PCIe SSDs you actually do get some thermal throttling. Here's a review of the Samsung SM951 where in just over 2 minutes of sequential write testing the card reached a throttle temperature of 82C and throughput dropped from 1500MB/s to 70MB/s (http://www.legitreviews.com/samsung-sm951-512gb-m-2-pcie-ssd...). I'd call that a noticeable dropoff in speed. Yes, I realize that article is talking about SSDs not SD cards. The relevant difference here is that the SSD is substantially larger with likely better heat dissipation.

Of course, the maximum bus speed of SD cards right now (including the UHS-II hardware change to add additional contacts) is only ~300MB/s, with a more practical top speed of ~150MB/s to allow both reading and writing. Maximum power consumption of UHS-II SDXC cards is 2.88W, which is actually fairly significant when you consider the volume of the cards - it's not a lot of power, but it's also not a lot of thermal mass.

My guess is that they mean relative to capacity. If the card is simply the same speed at a card 1/4 the capacity, that means you can read out only 1/4 as large part of the unit per unit of time.

Apart from the thermal throttling suggested elsewhere, there's also the bus speed, as well as the controller on the card. It's possible they could speed it up, but it's just as likely that they've just added 4x the same flash with a controller with the same read/write performance.

SD cards != SSDs. The applications they are used in tends to be more limited by capacity than speed, and they evolve accordingly.

I know some DSLR's have dual SD's in them, could we see an era of SD RAID? Weather thats all on one card or three separate cards striped with parity?

I'd also think the camera could act as a decent heatsink to disperse hear generated from the SD IC.

You've been able to buy SD and MicroSD raid devices for a while.

Here's one with a SATA interface: http://www.aliexpress.com/item/Del-10-x-Micro-SD-TF-Memory-C...

Here's one with a USB interface: http://alfa-media.com/products/tf%20raid.html

I've never used one, but they look scary.

Good grief, things have moved on somewhat quickly since I last looked. As you say, some of those are scary indeed!

I didn't take the quoted text as a suggestion that the drive would be slower in any absolute terms. 'Comparatively' can be an ambiguous term - compared to what?

I read it to mean compared to smaller SD cards, which is also the only reasonable comparison here. I just re-read it and I actually can't see what else it could be referring to.

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