Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

A2-class microSD cards offer no better performance for the Raspberry Pi

jeffgeerling.com

Post reply on HN
Print view View original

31–40 of 112 posts

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#31

Post by kup0 »

geerlingguy wrote: post #29
NikolaeVarius wrote: post #23

Earlier quoted context omitted.

Does /boot get read/written to enough where this is not "good enough"

It doesn't, but in my informal tests (I haven't had time to set up a thorough benchmark) real-world usage of an external USB 3.0 SSD (testing with a cheap Kingston SSD, though, and a cheap USB SATA interface) is only marginally faster than a Samsung Evo+ microSD card.

I wonder if this is also due to the fact that many desktop SSDs do not focus on 4k read/write performance. This is one big area where nvme SSDs seem to have an advantage, their 4k read/write is usually significantly higher than that of other SSDs (at least from benchmarks I've seen).

Maybe even a lower end nvme ssd + usb enclosure would be the way to go to get the best performance.

Unless there's something about the USB interface itself that kills random 4k r/w performance?

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#32

Post by jononor »

djsumdog wrote: post #18

I'm surprised we haven't seen a smaller than M.2 form factor for SATA on embedded devices. It seems like the big limiter on devices like the Raspberry Pi and others are the sd cards/emmc modules, since the amount processing power and ram have been continually going up. If you need disk performance on the Pi 4, wouldn't it make more sense to only keep the kernel,initrd on the sdcard and mount the primary filesystem of…

General practice in embedded is to avoid writing to disk as much as possible. Data collection is mostly done by sending it to the cloud for storage there. However 'edge processing' and 'edge storage' are hot topics, so there will probably be more work in this area. Some of the surveillance camera vendors are showing interest in this, since it would be beneficial to reduce data needed to be sent. Especially since vast majority of the data is never looked at, or only looked at once (human/machine event detection). But one has the (fundamental?) problem that the sensor is often installed in an adversarial environment. Would be sad to try to pull data after a crime, only to realize the camera storage was destroyed.

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#33

Post by jononor »

jws wrote: post #30
geerlingguy wrote: post #25

Earlier quoted context omitted.

Good chance that doesn't trickle down to the microSD interface; it seems like the best performance improvements are reserved for the full-size SD cards, likely because they can fit more thermal mass and connection pins in the larger case.

The term you want is “microSD express”. That is the standard for PCIe and NVME on microSD cards. It specs out at about 1GB/second transfer rates. Fun engineering decisions: It can use RAM from the hosting computer to store its logical block mapping tables so it doesn’t have to have DRAM onboard for that. That’s a clever way to use what the host has in abundance to avoid putting it on the price and volume constrained…

Solder the microSD and use the solder-points for thermal connection to the board, like for most other medium-power ICs. It is also cheaper than a socket.

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#34

Post by jononor »

jononor wrote: post #32
djsumdog wrote: post #18

I'm surprised we haven't seen a smaller than M.2 form factor for SATA on embedded devices. It seems like the big limiter on devices like the Raspberry Pi and others are the sd cards/emmc modules, since the amount processing power and ram have been continually going up. If you need disk performance on the Pi 4, wouldn't it make more sense to only keep the kernel,initrd on the sdcard and mount the primary filesystem of…

General practice in embedded is to avoid writing to disk as much as possible. Data collection is mostly done by sending it to the cloud for storage there. However 'edge processing' and 'edge storage' are hot topics, so there will probably be more work in this area. Some of the surveillance camera vendors are showing interest in this, since it would be beneficial to reduce data needed to be sent. Especially since vast…

Many embedded applications are also not particularly form-factor constrained. A good security camera lens is often easily bigger than a couple of 2.5" hard-drives and a medium sized single-board computation. Heck, just wiring boxes for an industrial sensor system, are can often bigger than 10s of 3.5" disks.

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#35

Post by megous »

A2 needs support in the Linux kernel. It's not there, yet.

https://github.com/ThomasKaiser/Knowledge/blob/master/articl...

"A2 promises even better performance with 4000/2000 read/write IOPS minimum but there's a problem since as outlined by the SD Association A2 cards show "much higher performance than A1 performance by using functions of Command Queuing and Cache".

Cache and Command Queuing require host (driver) support since the host needs to activate those new features first. The cache feature on A2 rated cards makes use of volatile RAM on the card requiring the host to learn new commands to issue flushing the cache (involving the risk of data losses -- for details see especially chapter 4.17 in Physical Layer Simplified Specification 6.0)"

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#36

Post by megous »

dkersten wrote: post #11
stefan_ wrote: post #2

Testing microSD card speed on a Mac is rather pointless because performance is (severely) limited on the Raspberry Pi through it's terribly slow interface, not necessarily the actual card. Remember RPi 1-3 use a plain SPI interface, and even the new 4 only has UHS-1.

He explained in the article why he did this: to check if the manufacturers claims are incorrect, or if its a RPi hardware issue.

It's neither.

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#37

Post by ggg3 »

sd card performance specs are all a joke.

they are "at most" some speed. What even is the point of writting such spec?

the car analogy would be if you measure some car going down a hill (doesn't even matter if tumbling and killing everyone inside), measuring that it was 300mph and then advertising it as "speeds of 300mph!!!"

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#38

Post by geerlingguy »

megous wrote: post #35

A2 needs support in the Linux kernel. It's not there, yet. https://github.com/ThomasKaiser/Knowledge/blob/master/articl... "A2 promises even better performance with 4000/2000 read/write IOPS minimum but there's a problem since as outlined by the SD Association A2 cards show "much higher performance than A1 performance by using functions of Command Queuing and Cache". Cache and Command Queuing require host (driver) su…

So is there any kind of device able to use A2 cards at the rated performance yet? I can't get anything better on my Mac with multiple readers (USB 3.0 and 3.1), and I'm guessing if I tried on the reader in my 1 year old Dell XPS, I'd get the same.

What good is a performance designation (A2) if no device in the real world supports it?

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#39

Post by monocasa »

stefan_ wrote: post #2

Testing microSD card speed on a Mac is rather pointless because performance is (severely) limited on the Raspberry Pi through it's terribly slow interface, not necessarily the actual card. Remember RPi 1-3 use a plain SPI interface, and even the new 4 only has UHS-1.

Rpi1-3 definitely have an MMC controller.

Re: A2-class microSD cards offer no better performance for the Raspberry Pi

#40

Post by cameronbrown »

ggg3 wrote: post #37

sd card performance specs are all a joke. they are "at most" some speed. What even is the point of writting such spec? the car analogy would be if you measure some car going down a hill (doesn't even matter if tumbling and killing everyone inside), measuring that it was 300mph and then advertising it as "speeds of 300mph!!!"

Also how ISP speed is measured ;)
Post reply on HN