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HawaiianPi
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Should you buy an A2 performance rated SD card?

Sat Apr 27, 2019 3:40 am

The short answer:
No, absolutely not! Not for your Pi or any other device you currently own (at the time of this post).


The long answer:
After getting very poor performance from an A2 card I ordered from Amazon, I was thinking about ordering direct from SanDisk (to ensure I didn't get a fake), but some interesting things happened along the way...

First I should tell you I ordered a 128GB SanDisk Extreme A2 micro SD card from Amazon and received it a few days ago. I was planning to test it in my Pi 3B+ and report my results here, then use it in my HP x2 Chromebook (Intel 7th Gen hardware). I wasn't expecting to get max performance out of the card (160MBps read/90MBps write), but I was expecting it to be faster than my A1 rated cards.

Initial testing was done on my gaming laptop (faster 7th Gen Intel hardware), and the results were puzzling. The Extreme A2 card was not only much slower than published specs, it was much slower than my A1 rated cards. Sequential read and both read & write IOPS were over 20% lower than my SanDisk Ultra A1 cards.

I ran several fake card test programs, and they all seemed to think the card was legit. Chip ID indicated a SanDisk product, and true capacity was 119.5GB, which is correct for a "128GB" card (due to the misleading way storage companies measure capacity).

I emailed SanDisk to inquire about my poor performance and ask if A2 cards required special hardware or drivers for better performance. I also sent detailed pictures of the card to see if they could identify it as a fake. The reply I got didn't really address my question about special hardware or drivers, but did suggest I might get better performance with their Mobilemate USB 3.0 micro SD card reader. They also said the card looked real, and the benchmark results I included seemed low and offered to issue an RMA if I wanted to send the card in as defective.

At this point I was pretty sure I had a genuine SanDisk card (still think that) and that the card was defective (not so sure about that now...).

I did some searching online and found a few other SD card benchmark results where A2 cards performed worse than A1 cards, so my results seemed to be what others were finding as well.

While poking around on SanDisk's site I noticed that the specs on sandisk.com (160MBps read/90MBps write) did not match the specs for the same card on their shop.sandisk.com web store (90MBps read/60MBps write). So I tossed another support question their way, again asking if A2 cards required special software or hardware to perform well, and again they kind of sidestepped the question by recommending the Mobilemate card reader (although the second answer did state that the Mobilemate was required for maximum performance). They also said the specs on the web store were wrong (160/90 is correct) and they would get that fixed.

So now I'm thinking that card I returned to Amazon yesterday might not have been defective, and that A2 cards not only require special hardware and/or software for maximum performance, they actually perform WORSE than A1 cards without it. This seems to be backed up by results others have experienced when testing A2 cards.

While wandering around the world wide web (of misinformation and despair) I found an article in which SanDisk specifically said that A2 cards were faster than all current mobile technology, and no phones or tablets available now could achieve maximum performance. They tried to spin this as a good thing, and didn't say anything about them performing worse in current tech, but I wonder...

And then, while working my way through "the fine print" on SanDisk's site I stumbled upon this:

For 128GB-1TB: Up to 160MB/s read speeds, engineered with proprietary technology to reach speeds beyond UHS-I 104MB/s,
requires compatible devices capable of reaching such speeds.
.

As far as I can find, the only "compatible device" is the SanDisk Mobilemate USB 3.0 micro SD card reader (mixed reviews on Amazon).

But now I'm wondering if that "proprietary technology" actually performs worse in non-compatible devices? :?

So was the card I returned really defective, or is A2 tech not ready for primetime (requires "compatible devices" to not perform like crap)?

My recommendation at this point in time is to avoid A2 cards. You'll spend more money and get less performance.

Get the SanDisk Ultra A1 or Ultra Plus A1 cards. They're affordable and fast!


Off topic side note:
Amazon has really streamlined their return process. When I clicked on the link to return the card I was offered a new option to drop it off at a UPS store with a code. No packing or even printing a label required. Amazon sent a QR code to my phone, and I just let them scan the code at the UPS store and handed them the card. They packed and shipped it for me. That was quicker and easier than returning something to a local store.
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Andyroo

Re: Should you buy an A2 performance rated SD card?

Sat Apr 27, 2019 7:51 am

Thanks for the heads up and posting here. I’m down to my last spare SD card and being lazy was going to order some next week rather than recycle older ones and had looked for the A2s. I’ll stick to the A1 cards from SanDisk for now.

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bensimmo
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Re: Should you buy an A2 performance rated SD card?

Sat Apr 27, 2019 9:45 am

We have me ruined that before when they first came out.
It needs 'stuff' to make them work, where A1 doesn't as that's just a physical spec.

You might have stumbled on it that at some point.
What was surprising at the time is they didn't just default to A1 spec speeds.
At that point we were hoping a 'driver' would come along to identify A2 cards at the host end and do the 'stuff'.
That's as technical as I can get.

From the official sdcard.org
"A2 performance is available only the combination of A2 supported host and A2 supported card. "
https://www.sdcard.org/developers/overv ... index.html
And the white paper is there if you are interested.

Also of note to Pi users is the A2 features are caching and command queuing, which of course adds a layer of dataloss on power out if the host hasn't flushed the A2 cards internal flash.
At least that's how I see it.

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DarkPlatinum
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Re: Should you buy an A2 performance rated SD card?

Sat Apr 27, 2019 10:16 am

Has anyone tested the sandisk extreme pro? https://www.amazon.co.uk/SanDisk-Extrem ... 58&sr=8-18
1 * Raspberry Pi Zero W, 1 * Raspberry Pi 2, 1 * Raspberry Pi 3 1 * Raspberry Pi 3B + :mrgreen:

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escobarrr
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Re: Should you buy an A2 performance rated SD card?

Sat Apr 27, 2019 6:42 pm

it's been a long time since i wanted to buy the sandisk extreme pro but i do not know if it's really worth it.

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LTolledo
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Re: Should you buy an A2 performance rated SD card?

Sun Apr 28, 2019 3:43 am

For me its Class6 microSD for non-critical headless setup, Classs10 for NAS server.

No plans on getting A2 cards for setups on the RPi2B v1.2, RPi3B and RPi3B+ as those are already converted to USB SATA /USB mSATA.
The A1 microSDs formerly used on those setups are now serving as backups.
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HawaiianPi
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Re: Should you buy an A2 performance rated SD card?

Sun Apr 28, 2019 9:26 am

DarkPlatinum wrote:
Sat Apr 27, 2019 10:16 am
Has anyone tested the sandisk extreme pro?
I doubt you'd gain much performance over the less expensive Ultra A1, because the Pi's SD card interface doesn't support high speed modes. Read speed will certainly be bottlenecked, but you might gain a little in write performance. The main point of getting an A1 card is the higher IOPS, not the faster read/write speeds.

For the price of that Pro card you could probably pick up a 120GB SSD, which would boot slower but perform better once the OS was loaded. Of course the tricky part of USB booting a Pi form an SSD is finding a compatible USB-SATA adapter.

bensimmo wrote:
Sat Apr 27, 2019 9:45 am
What was surprising at the time is they didn't just default to A1 spec speeds.
That was my thought as well. I didn't expect to get full A2 performance, but I was expecting some improvement over A1. Very disappointing it's so proprietary. And pretty shady marketing to not warn people that A2 cards won't work properly with their existing hardware. Fine print in the product info says A2 compatible devices are required for maximum performance, but nowhere does it say it will perform worse without it.
Dilbert_marketing_2.gif
Dilbert_marketing_2.gif (30.82 KiB) Viewed 2340 times

Oh well, lesson learned. And of course Amazon is now out of stock on the A1 card I should have ordered in the first place. :(
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jahboater
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Re: Should you buy an A2 performance rated SD card?

Sun Apr 28, 2019 11:24 am

HawaiianPi wrote:
Sun Apr 28, 2019 9:26 am
Oh well, lesson learned. And of course Amazon is now out of stock on the A1 card I should have ordered in the first place. :(
Thanks anyway for the info.
I'll stick with A1 class cards for now.

For me, write speeds are not relevant since as long as you are writing less than 600MB or so in one go, it all goes straight into the disk cache and is effectively instant. Reads often must be waited for, but only the first time the file is read and its not in the cache.
Random 4K reads that the OS uses, are the most important.

cspan
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Re: Should you buy an A2 performance rated SD card?

Mon Apr 29, 2019 1:38 am

Thanks for posting your experience. Before I read your full (top) post, I thought it was a case of fakes being sold via the River Site. I have lost a lot of trust with them of late.

However, it seems you went to great lengths and determined you got a genuine product, but it is not performing as expected. Sandisk's constant pushing of Mobilemate suggests to me that they are defining a new proprietary standard of which they are the gatekeeper / toll collector. Perhaps those making devices that can accept A2 cards will have to play ball with them to unlock the higher levels of performance. I am surprised if SD released this just with an A2-capable card reader, and that there aren't more devices optimized to accept A2 cards yet. You'd think they'd time the rollout to coincide with products that can claim the advantage.

In any case, yes, I agree with you, one would expect that SD would want a non-A2 device to at least get A1 performance. It's not to their advantage to hurt their own reputation by having customer experiences be much worse than expected. Maybe they couldn't do it ... it would be surprising though. Risky play.

You mention Amazon being out of A1 cards. Have you checked Costco? In January they were selling 2x 64GB A1 cards for $25. That said ... they don't have them now, at least not in stores ... A2 has supplanted them. But Costco online - they're now down to $22:

https://www.costco.com/SanDisk-Ultra-Pl ... 65387.html

Hopefully A1 handles the wear leveling better etc. but at that price it can be thought of as a consumable item!

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bensimmo
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Re: Should you buy an A2 performance rated SD card?

Mon Apr 29, 2019 10:41 am

It is not SanDisks standard but an SD standard, nothing proprietary.
It actually, reading their documents, looks like Google pushed for most of the changes to get decent cards for mobile phones and tablets.

Anyway it's part of the SD 6.0 standard I think.
(A1 was SD 5.1 standard).

But like UHS-II with its extra pins, stuff need to support it (it may be this speed that the card reader 'support script' is being mentioned, probably a bit like RPi and the use official PSU problem solving.)

If anyone knows if the big standard uSD slots can support A2, or which kernel has A2 support in, or if it needs turning on...

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Re: Should you buy an A2 performance rated SD card?

Mon Apr 29, 2019 12:29 pm

bensimmo wrote:
Mon Apr 29, 2019 10:41 am
It is not SanDisks standard but an SD standard, nothing proprietary.
It actually, reading their documents, looks like Google pushed for most of the changes to get decent cards for mobile phones and tablets.

Anyway it's part of the SD 6.0 standard I think.
(A1 was SD 5.1 standard).

But like UHS-II with its extra pins, stuff need to support it (it may be this speed that the card reader 'support script' is being mentioned, probably a bit like RPi and the use official PSU problem solving.)

If anyone knows if the big standard uSD slots can support A2, or which kernel has A2 support in, or if it needs turning on...
It appears you are correct - so that's good news. Here's what I found at the SD Association website:

https://www.sdcard.org/developers/overv ... index.html

So the "A" is for Application Performance Class. It appears to be specifically geared for applications running from the card, as opposed to simply storing and reading files like images, pictures, music, etc. Seems like it's a welcome direction for what the Pi needs, so long as the Pi is designed to run its OS from a microSD card slot. For A2, it does mention command queueing and cache, which I think were brought up in another thread as things to consider in terms of timing power off after shutdown, or where loss of power may occur.

It is still curious why an A2 card would perform worse than an A1 card in a non-A2 device. Nevertheless, if the touted performance improvement of 2.67x random r/w over A1 can be realized, that would be a wonderful thing if the next Pi can take advantage of it (assuming it still relies on microSD to keep its form factor).

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HawaiianPi
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Re: Should you buy an A2 performance rated SD card?

Mon Apr 29, 2019 7:41 pm

cspan wrote:
Mon Apr 29, 2019 1:38 am
In any case, yes, I agree with you, one would expect that SD would want a non-A2 device to at least get A1 performance. It's not to their advantage to hurt their own reputation by having customer experiences be much worse than expected. Maybe they couldn't do it ... it would be surprising though. Risky play.
It does seem risky from a marketing/reputation standpoint, but I assume the thought process was that most people would be upgrading from a standard Class-10 card, and comparing performance to that (not A1 cards). A2 cards are faster than C10 cards, so it's pretty sketchy marketing to entice people to spend more on a card that will perform worse than the cheaper A1 alternative. Looking at the percentage of bad reviews on A2 cards, it is higher than A1, but still mostly positive. So the sketchy marketing seems to be working.

cspan wrote:
Mon Apr 29, 2019 1:38 am
You mention Amazon being out of A1 cards. Have you checked Costco? In January they were selling 2x 64GB A1 cards for $25. That said ... they don't have them now, at least not in stores ... A2 has supplanted them. But Costco online - they're now down to $22
Costco has put the 2x64GB Ultra Plus A1 on sale for less than $20 a few times in the past. I got it last time it was <$20, and at under $10 for a 64GB A1 card it's a great deal! The Ultra Plus has higher sequential write speeds than the Ultra, but other than that they perform similarly.

Before I got the 128GB Extreme A2 card I was also considering the 256GB Ultra A1 card (which was only a little more), but that went out of stock, then the price jumped up. :cry: So now I don't know what I want for my Chromebook. Guess I'll just stick with the 64GB Ultra Plus A1 card for now (the other 64GB Ultra Plus A1 card is in my Creeper Pie Minecraft SMP server).

cspan wrote:
Mon Apr 29, 2019 1:38 am
Hopefully A1 handles the wear leveling better etc. but at that price it can be thought of as a consumable item!
Wear levelling is an optional feature that SD card makers can implement. It's not required by any official SD card specification. SanDisk has stated that all of their cards support wear levelling (not just A1 or A2 cards).
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stuartiannaylor

Re: Should you buy an A2 performance rated SD card?

Tue Apr 30, 2019 2:19 pm

DarkPlatinum wrote:
Sat Apr 27, 2019 10:16 am
Has anyone tested the sandisk extreme pro? https://www.amazon.co.uk/SanDisk-Extrem ... 58&sr=8-18
Been raving about the performance of the 32gb a1 Pro.
viewtopic.php?f=63&t=238959
You can pick that up for nearer £10 but aint paying £30 for an SD card for a Pi.
https://www.picstop.co.uk/microsd-sdhc/ ... fTEALw_wcB

But near £15 can buy a 120gb SSD & £5 for a USB Sata even if its a tug of war with the ethernet.
https://www.amazon.co.uk/Silicon-Power- ... 07KR25Q72/

PS this guy has thrown up a good series of articles and a common bench script
https://jamesachambers.com/raspberry-pi ... ng-script/

Also prices have dropped even lower where a 120gb SSD is actually quite a bit cheaper than a 128gb A1 micro SD.

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Re: Should you buy an A2 performance rated SD card?

Sun Sep 15, 2019 8:18 am

Got tremendous performance gain using A2 sd card, (so I disagree with OP).

Moving from Toshiba M302 (fast sequential but no slow 4k), to Sandisk Extreme A2 / V30, the performance gain was > x20 for some file operations. Amazing performance, no need for external SSD and fast net i/o since USB/ethernet-bus not congested.

Board: 3b

regards,
/t

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Re: Should you buy an A2 performance rated SD card?

Sun Sep 15, 2019 5:48 pm

teson2000 wrote:
Sun Sep 15, 2019 8:18 am
Got tremendous performance gain using A2 sd card, (so I disagree with OP).

Moving from Toshiba M302 (fast sequential but no slow 4k), to Sandisk Extreme A2 / V30, the performance gain was > x20 for some file operations. Amazing performance, no need for external SSD and fast net i/o since USB/ethernet-bus not congested.

Board: 3b

regards,
/t
The M302 is not an A class card, not even A1.
~We are talking A1 card, of the same brand, compared to A2 here.

(though the title may be misleading in that respect)

pica200
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Re: Should you buy an A2 performance rated SD card?

Sun Sep 15, 2019 7:06 pm

I saw this thread only now as it was bumped and i agree with not getting A2 cards until they are supported. One thing i don't agree with is this:
(due to the misleading way storage companies measure capacity)
The only one wrong here is Microsoft because they display misleading units. Kilo-/Mega-/Gigabytes and so on is a power of 10! Not power of 2! See this table. I don't want to defend the storage industry but unfortunately they right and actually use the units correctly. If you calculate the size according to this you will actually get exactly what's advertised.

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HawaiianPi
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Re: Should you buy an A2 performance rated SD card?

Sun Sep 15, 2019 8:07 pm

teson2000 wrote:
Sun Sep 15, 2019 8:18 am
Got tremendous performance gain using A2 sd card, (so I disagree with OP).
You need to test against an A1 app performance rated card, not a standard Class-10 card. A2 cards are faster than standard cards (and I said so above), but A1 cards are faster and cheaper on Pi computers (and most other devices, with the exception of sequential write).

pica200 wrote:
Sun Sep 15, 2019 7:06 pm
The only one wrong here is Microsoft because they display misleading units. Kilo-/Mega-/Gigabytes and so on is a power of 10! Not power of 2! See this table. I don't want to defend the storage industry but unfortunately they right and actually use the units correctly. If you calculate the size according to this you will actually get exactly what's advertised.
Computer storage based on powers of 2 has a long history that far precedes terms like mebi or gibi (from the table in the link you posted), which were adopted in the late 1990s. Prior to that it was accepted that telecommunications used powers of 10 and computers used powers of 2 when calculating large data quantities.

The tebi, gibi nonsense was a failed attempt to alleviate the discrepancy, but in the end it only caused more confusion and gave the storage industry license to mislead customers. However, the courts agree with my assessment. Seagate was sued over the discrepancy and lost (misleading advertising) but apparently they didn't lose enough, because they are still doing it (with a disclaimer on the packaging).

And it's not just Microsoft Windows that uses powers of 2 for storage sizes. Many other operating systems do it (including many Linux distros).

If I purchase 16GB of system RAM, I get 17,179,869,184‬ bits of system RAM. If I purchase a 16GB micro SD card, I get (roughly) 16,000,000,000 bits of storage. So the fact is that I cannot store the contents of 16GB system RAM to a 16GB storage device, and that is misleading.
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