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I'm currently using my Pi4 as a NAS with OpenMediaVault and i was thinking about moving the OS from the SD Card to an external SSD on one of the USB 2 Ports, since both USB 3 Ports are being used for my NAS Drives.

I Know that SD Cards aren't really meant to be used 24/7, so i just wanna make sure that i'm not going to have buy new SD Cards every now and then. I don't know if an SSD would be to slow when it's connected with USB 2 tho, i don't know a lot about that stuff tbh.

What do you guys think?

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    "I Know that SD Cards aren't really meant to be used 24/7" -> This is apocryphal. I am sure that many of the regular users here would attest to running Pis 24/7 for years without replacing the SD card. Of course what you are doing with it is the biggest factor, but for an NAS with the storage on other peripherals you will be fine, ie., that is a 6 vs. 2x3 scenario. Do whatever appeals to you, but if you want an honest opinion I think in context the difference is probably not worth the extra hardware and hassle -- you won't see any real practical difference.
    – goldilocks
    Jul 30, 2020 at 20:38
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    If you want to make sure the sdcard will work long you can use one optimized for durability. Or/additionally you can reduce the number of write requests, if you want down to zero. There are plenty of guides showing how to disable certain logs, use ramdisks for unimportant logs and so on. You can even make the system partition read-only.
    – Robert
    Jul 30, 2020 at 21:19

3 Answers 3

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I'd suggest using an SD Card. Like goldilocks mentioned, you won't have to keep replacing your sd card if it isn't doing some extremely heavy work, if you're just running a NAS you can use an SD card from a reputed brand and get another free USB port.

If longevity is your concern you're not getting any large benefit form it. Speed shouldn't be your concern because a NAS won't be utilizing that speed. The only advantage would be the bootup time.

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USB 2.0 has a maximum bandwidth of 480Mb/s, or 60MB/s although speeds closer to 30MB/s are common. The raspberry pi foundation says that any SD card will work and give examples of cards that operate at 4 and 10 MB/s so a USB 2.0 SSD should have sufficient speed.

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  • Oh, so an SSD on usb2 will actually be faster than the SD Card? That's good to know, guess im gonna go get a cheap SSD. Thank you very much! :) Jul 30, 2020 at 20:29
  • "USB 2.0 has a maximum bandwidth of 480Mb/s" This is a theoretical limit and you are unlikely to see speeds beyond half that (30 MB/s) especially on a Pi. For the model 1 and 2 this means they are somewhat faster, as SD reads peek at 20-25 MB/s. For the 3 I believe something changed allowing faster cards to work closer to their potential. So it is I think possible to have a Pi where the SD card out performs a USB 2.0 drive, but generally it will be the other way around.
    – goldilocks
    Jul 30, 2020 at 20:45
  • "any SD card will work … so a USB 2.0 SSD should have sufficient speed" What has this to do with the Question? SD Cards do not use USB interface.
    – Milliways
    Jul 31, 2020 at 0:13
  • Since any sd card will work, even at speeds of 4MB/s, any USB 2.0 SSD should work because it will have a speed > 4MB/s Jul 31, 2020 at 2:31
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If you don't care about the writing speed an SD-card should do the work. For me, a 128GB from SanDisk was too slow. The way I solved I purchased ArgonOne M.2 Case which supports SSD128gb to USB3.0 board and that way I installed an SSD where the OS is installed. Since the case is in aluminum and comes with a fan I manage to get both static and active cooling, 7 times faster writing and reading speed, and the SD card is used just as a storage. Highly recommended. Adding a link just as a reference: https://www.microcenter.com/product/630108/argon40-one-m2-case-for-raspberry-pi-4

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