[Discuss] More ZFS Questions

[markw at mohawksoft.com]

> On Sat, 20 Aug 2022 16:14:08 -0700
> Kent Borg <kentborg at borg.org> wrote:
...
> My limited experience with Raspberries Pi and USB flash is it will
> always fail under sustained high load. Either insufficient power will
> cause data loss or overheating components will cause data loss.

Funny enough, an SD card gets destroyed by the RaspberryPI, and its not
the heat or the power, it is the nature of SD cards.

Each "sector" or "block" on an SD card can only be modified so many times,
its really quite limited. On the SD card is a management system that
manages the flash memory "blocks." They have "wear management" algorithms
that mask out bad blocks and rotate through the whole pool of blocks, but
eventually you will start writing to blocks that can no longer take a
write, and this is when you get a bad sd card.

Better SD card brands may advertise something like 32G, but will have a
percentage of over allocation to handle wear.

The problem is that SD cards are designed for things like cameras and
music players where modification is not usually all the often.
Unfortunately for the RaspberryPI, in the default configuration, the SD
card is used for logs, state, swap, and stuff like that. An active
RaspberryPi can chew through an SD card in a month.

To preserve the SD card, you should mount it read-only and only allow
upgrades to write to the SD card. raspi-config in modern versions has this
option.

I did something different. I formatted my SD card, then I copied the "/"
partition to a 250G USB SSD, modified /boot/cmdline to mount off the USB
disk (and updated the /etc/fstab) so that when it boots /boot is read-only
and "/" and "swap" are on the SSD.
>
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