eMMC vers SD card

    • OMV 4.x

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    • richprim wrote:

      What is the advantage of a eMMC over a SD card for the OS?
      It's not possible to answer this question since it depends on the products used.

      Usually eMMC is faster and more durable but some SBC vendors use sometimes EOLed eMMC that is slow as hell so almost every SD card outperforms it (applies to recent Banana Pi models for example).

      Both eMMC and SD cards are usually accessed via an SDIO bus and usually SD cards are bottlenecked since most hardware vendors only support the slowest DDR50 mode limiting sequential performance to ~23 MB/s and also limiting random IO performance at the same time (see this comparison of DDR50 with SDR104: forum.armbian.com/topic/1925-s…ab=comments#comment-54071).

      Common eMMC implementations use a wider bus and faster modes so depending on the hardware sequential transfer speeds max out at 80 MB/s with most common cheap SBC or even 300 MB/s with high-end (Rockchip) single board computers (see numbers and links here). Also random IO performance is usually a lot higher than the average SD card (but why buying average AKA crappy SD cards when we can buy A1 rated SD cards today?)

      Durability depends on the flash chips and controllers used. Some premium flash vendors provide numbers (TBW -- TB written, some sort of endurance rating), some others don't. For example I wouldn't trust that much into the cheap FORESEE eMMC modules available for Rock64 and RockPro64 for the simple reason I've not seen them on premium products so far. I would rely on SD cards instead. But not crappy cards but SanDisk Extreme Plus A1 or something similar. That's not backed by evidence but just an assumption/feeling.

      The post was edited 1 time, last by tkaiser ().

    • richprim wrote:

      What is the advantage of a eMMC over a SD card for the OS?
      Now the same question answered with context OMV: it's 100% irrelevant as long as you enable our flashmemory plugin and disable monitoring (default on all the OMV images for ARM boards).

      With OMV and flashmemory plugin enabled both performance and durability of the rootfs doesn't matter any more. Also NAS performance will not vary.

      It's irrelevant so simply choose the cheapest option as long as you ensure you buy reliable storage and no counterfeit products (this is the other real eMMC advantage today: unlike SD cards where the market is flooded with fake/counterfeit products this still does not seem to happen with eMMC modules. You can assume that you always get genuine eMMC modules but I would always test with either F3 or H2testw prior to usage. It's stupid to trust into any flash storage product being genuine and not fake. You need to test)
    • richprim wrote:

      So far I have not had any SD wear out on me

      One detail I forgot above: Updating OMV and the Debian base OS is always stress for the storage media. So while SD card or eMMC performance is pretty much irrelevant for normal operation this changes when updates are to be installed. Using slow/old/crappy SD cards this can take ages and also slow down OMV operation while updating since the OS is stuck on IO (I tried to explain here why)

      As explained here and reported by @wolffstarr there: Especially an OMV release upgrade (omv-release-upgrade) can end up with a bricked installation with 'bad' SD cards since the card might not survive the stress (same is true for eMMC but usually eMMC lasts a lot longer than el cheapo SD cards).

      My only recommendation today is to buy new SD cards that are compliant to A1 or A2 performance speed class: forum.armbian.com/topic/954-sd…findComment&comment=49811
    • As a note, "bad" is not necessarily what you think it is, either. For instance, the SD card that I had fail on me was a Samsung 16GB, it just happened to be an older one. You are flat-out playing with fire, even with folder2ram, if you take the SD card you've "always used" that's been sitting in your Pi for 3 years and try and do an omv-release-upgrade. Make a backup image first, write that to a brand new card, boot with it, and THEN do an upgrade if you want everything to stay in place.