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Nearly all the questions and posts around the internet discuss sd card vs SSD which should be fairly obvious, my question is unique? If someone knows a discussion of this elsewhere please link me.

I'm wondering about boot/full system SSD vs boot SD CARD (minimal writing) + SSD for majority of tasks. Would the latter be more reliable because the sd card of the pi is treated as a base operating system, without being written to much/at all other than updates? (I've put logs on ramdisk)

Would SSD as single only drive/boot drive still be more reliable even with a micro sd card being virtually unused?

example of devices: sd card: sandisk extreme pro A2 rated ssd: samsung evo 960

I've had random cheap sd cards that have lasted since pi1 with constant use and SSDs that have died in a few months with virtually no use, so I am aware of these flukes.

SSD would be getting moderate use in both cases, as file server (mostly read from) and mail server (small writing/reading) about 4 users.. I'd estimate 1gb written a day.

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  • For the mail server use case, I read one can't have have the noatime and nodiratime flags for the partition (which reduce writes/prolong drive life), since these file attributes are often needed by mail clients. Not sure how much truth there is to that, but I'm curious how you're mounting your SSD..? Aug 2, 2020 at 0:18
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    @unknownprotocol probably use: "defaults,noatime", relatime was used to help fix that issue but I haven't encountered that for mail servers in like 10+ years. I forgot what used to require access times..
    – someguy
    Aug 2, 2020 at 0:32

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A normal cell in an SD card should have a write of about 25 000 times (better for high quality, lower for bad quality). In addition, logic re-routes the used cells, and good quality cards have some additional room (sometimes up to 4G for a 16G card).

Single level NAND on an SSD can have something between 50 000 and 100 000 writes. SSD's use the same kind of logic to re-distribute the writes.

Would SSD as single only drive/boot drive still be more reliable even with a micro sd card being virtually unused?

From the figures above, in theory, the SSD will last about twice as long. So, twice as reliable.

There are many discussions on how to prolong the lifetime of your SD card. They all amount to one thing: write as little as possible. That is consistent with the figures above. The instructions how to achieve this are sometimes complicated. It is easier to boot directly from an USB mass storage device than move all directories that write a lot only to that drive (/var/log for example)

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  • Yes and? That's covered basically what I already said in my questions
    – someguy
    Aug 4, 2020 at 1:36

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