4 ms·

I think they're saying it's the longevity, rather than the performance boost, that they're excited about.

geerlingguy 6y ago
That's how I read the grandfather comment too—a 3-4 GB/sec NVMe SSD wastes a lot of performance potential on a Pi, but the main thing that is nicer about even low-end SSDs is they have way better write/rewrite longevity than microSD cards, few of which are design in any way for general computing use. Most microSD cards optimize for only one thing—storing large, sequentially-written video files, then copying them off. Rinse and repeat. Even some of the fancy "100 MB/sec+" microSD cards only get like 1-2 MB/sec in random access patterns.
- megous 6y ago
  4k block random read on a regular A1 rated uSD card is 8MiB/s. I benchmark 11MiB/s on some of my Sandisks Ultras, depending on manufacturing date. Writes usually don't matter much, unless you use an inappropriate filesystem for a SD card or sync a lot. Longevity is longer for SSDs but it's not that bad for uSD cards either. If you setup your system so that there are no pointless writes all the time, they last 3-5 years, no problem, and probably more. The biggest benefit is that uSD cards are much lower power. And unless the use case is very storage heavy, like a constantly accessed database, or backups, SSD is just a waste of resources.
  - felipelemos 6y ago
    > If you setup your system so that there are no pointless writes all the time, they last 3-5 years, no problem, and probably more. Define pointless writes.
    - megous 6y ago
      Anything not related to your use case for the board. Random crap general GNU/Linux distros will do because this is not an issue, on usual HW.
  - erik 6y ago
    Consumer mircoSD cards commonly have firmware bugs. A Raspberry Pi running Linux will consistently trigger these bugs given enough time, even if you mount the card read-only. The nand is fine, but the card will be unreadable until reformatted. You might never see this from a single Pi running at home, but people who deploy large fleets of Pis inevitably run into these problems. Industrial microSD cards aren't perfect, but they are more reliable.
    - sgtnoodle 6y ago
      Removing an SD card from its socket during a write operation can actually brick the card enough to no longer work at the block level. Perhaps it's brand dependent, but I'm talking about a well known name brand. It's rare, but I know of a ziplock bag of bricked SD cards that shows it's not too rare. I suspect it occurs when a card loses power while in the middle of shifting data around for wear leveling purposes. Presumably, some internal data structure gets borked in a way that the card's embedded MCU firmware didn't anticipate and can't recover from.
      - erik 6y ago
        It doesn't even have to be during a write operation. Nand needs to be periodically refreshed after a read, so the controller can be shuffling data even on a read-only mounted card. I've read speculation that most consumer cards store their controller firmware on the same nand that is used as the general storage, and thus are prone to corrupting their own firmware if something goes wrong while shuffling data. Power loss is definitely a threat to an SD card in a Pi. But I've seen many cards go bad while the system is still running, so it's not the whole story. Weirdly, I've had a number of cards that entered a state where they would be inaccessible under Linux or Mac OS. But they could easily be recovered by a re-format under Windows. No idea why. Perhaps the manufacturers test a lot more thoroughly with Windows?
        sgtnoodle 6y ago
        That's a good hypothesis re: the MCU firmware on the NAND. If it's true that all NAND needs to be periodically refreshed, then it could be as simple as losing power while one of the firmware sectors is getting refreshed. That seems like an obscure enough scenario that there's dragons lurking around it. I like to imagine in my head that the MCU in an SD card can detect its voltage dropping quickly enough to get into a safe state most of the time. With all the recommended capacitance around the socket, it might actually have a few milliseconds to work with after external power loss. When you pull the card out of a socket, though, the MCU stops working before it has time to do anything about it.

That's how I read the grandfather comment too—a 3-4 GB/sec NVMe SSD wastes a lot of performance potential on a Pi, but the main thing that is nicer about even low-end SSDs is they have way better write/rewrite longevity than microSD cards, few of which are design in any way for general computing use. Most microSD cards optimize for only one thing—storing large, sequentially-written video files, then copying them off. Rinse and repeat. Even some of the fancy "100 MB/sec+" microSD cards only get like 1-2 MB/sec in random access patterns.

megous 6y ago
4k block random read on a regular A1 rated uSD card is 8MiB/s. I benchmark 11MiB/s on some of my Sandisks Ultras, depending on manufacturing date. Writes usually don't matter much, unless you use an inappropriate filesystem for a SD card or sync a lot. Longevity is longer for SSDs but it's not that bad for uSD cards either. If you setup your system so that there are no pointless writes all the time, they last 3-5 years, no problem, and probably more. The biggest benefit is that uSD cards are much lower power. And unless the use case is very storage heavy, like a constantly accessed database, or backups, SSD is just a waste of resources.
- felipelemos 6y ago
  > If you setup your system so that there are no pointless writes all the time, they last 3-5 years, no problem, and probably more. Define pointless writes.
  - megous 6y ago
    Anything not related to your use case for the board. Random crap general GNU/Linux distros will do because this is not an issue, on usual HW.
- erik 6y ago
  Consumer mircoSD cards commonly have firmware bugs. A Raspberry Pi running Linux will consistently trigger these bugs given enough time, even if you mount the card read-only. The nand is fine, but the card will be unreadable until reformatted. You might never see this from a single Pi running at home, but people who deploy large fleets of Pis inevitably run into these problems. Industrial microSD cards aren't perfect, but they are more reliable.
  - sgtnoodle 6y ago
    Removing an SD card from its socket during a write operation can actually brick the card enough to no longer work at the block level. Perhaps it's brand dependent, but I'm talking about a well known name brand. It's rare, but I know of a ziplock bag of bricked SD cards that shows it's not too rare. I suspect it occurs when a card loses power while in the middle of shifting data around for wear leveling purposes. Presumably, some internal data structure gets borked in a way that the card's embedded MCU firmware didn't anticipate and can't recover from.
    - erik 6y ago
      It doesn't even have to be during a write operation. Nand needs to be periodically refreshed after a read, so the controller can be shuffling data even on a read-only mounted card. I've read speculation that most consumer cards store their controller firmware on the same nand that is used as the general storage, and thus are prone to corrupting their own firmware if something goes wrong while shuffling data. Power loss is definitely a threat to an SD card in a Pi. But I've seen many cards go bad while the system is still running, so it's not the whole story. Weirdly, I've had a number of cards that entered a state where they would be inaccessible under Linux or Mac OS. But they could easily be recovered by a re-format under Windows. No idea why. Perhaps the manufacturers test a lot more thoroughly with Windows?
      - sgtnoodle 6y ago
        That's a good hypothesis re: the MCU firmware on the NAND. If it's true that all NAND needs to be periodically refreshed, then it could be as simple as losing power while one of the firmware sectors is getting refreshed. That seems like an obscure enough scenario that there's dragons lurking around it. I like to imagine in my head that the MCU in an SD card can detect its voltage dropping quickly enough to get into a safe state most of the time. With all the recommended capacitance around the socket, it might actually have a few milliseconds to work with after external power loss. When you pull the card out of a socket, though, the MCU stops working before it has time to do anything about it.