emmc also won’t eat itself as fast as sd cards.
You can mitigate that a bit by enabling fstrim options in your fstab I believe.
eMMC is essentially the identical thing to a microSD card, just as an SMD package instead of a card format.
I see some people have longevity problems with SD cards and better results with eMMC, but that’s likely due to using low-quality microSD cards.
@adcockm
Which card (brand / model) do you use?
@barry99705
How? They are technically identical…
eMMC - embedded MMC
This refers to basically what you can think of as an SD card that’s built into a motherboard (SD and MMC standards are very similar - enough that SD card readers can typically read MMC cards)
SD cards are limited to 4 data line, I suspect the CM4 uses 8 on the eMMC so you do get about twice the performance. Not sure life is any better.
hmmm, maybe I’m just remembering all the kingston sd cards I used to kill booting my old eeepc. They’d last about a year before they’d just become read only.
Technically yes, but SDXC cards can go up to 300MB/s and the latest generation (SDUC) will even allow for 985MB/s of max. speed. That should be enough for any application on SBCs.
I will probably use a SanDisk Extreme 128GB with 200MB/s which had cost me only 16 bucks a while ago.
@barry99705 I had this experience in the past, too. But since they are technically the same technology in a different package, I have to assume that they just used low-quality flash in the past. At a time, when high-frequency r/w was an edge case for microSD and most people were just saving camera photos on them.
True they are the same tech, but on the CM4 the eMMC uses all 8 data lines and on an SD card you only get 4. You get twice the bits per cycle. Does the CM4 support the SDXC ? when not using the eMMC?
i can confirm the 8gb cm4 lite works fine - typed this response on my uConsole with one installed.
Sorry, I completely forgot to respond to this… I use this Sandisk Extreme 400GB card (and used it for the test above).
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I am curious whether it is worth getting 8GB instead of the standard 4 GB. I would be ordering without the core and risking not being able to buy a CM4108000 before the kit arrives.
Just to confirm,
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if you have the 8GB 32GB eMMC CM4, and you don’t use the eMMC, it can still use the SD card?
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Does it automatically detect if there is no partition on the eMMC and then activates the SD card instead? And if not how does it decide to use the SD card if the CM4 has eMMC?
I only have eMMC CM4’s from past projects.
- So would deleting the partitions on the eMMC allow the UConsole to use the SD card?
no, if the cm4 has emmc you cannot use the sd card at all. clockworkpi didn’t add the functionality to flash the emmc or make choose between them.
The limitation for using the SD Card on emmc CM4s is actually due to how the CM4 is designed. The lanes for the sdcard is routed to the emmc instead
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thanks for reply
i’ll just flash the eMMC on a carrier board then.
wow this is shortsighted of the raspberrypi/broadcom designers. they should have added more lanes to that chip.
don’t get why it can’t just boot from eMMC first and SD second if its present.
wouldn’t have hurt them to add two more lanes for SDIO over GPIO on pins 22-27.
either way i get why clockworkpi did this, the CM4 lite is cheaper and more available and SD storage is a lot more space for the money, eMMC is way more expensive for a small amount of storage and not that much more speed (~18MB/s).
I suspect that the biggest reason is more people have SD card readers than CM4 IO boards.