Rootfs A/B vs. bootloader A/B

Hello,
In the documentation, there is not much differentiation between the two concepts (rootfs A/B and bootloader A/B) and sometimes the terms are used interchangeably.
I’m new to all of this, so can someone explain to me the difference, and how the two concepts are linked?
Thank you

Do you know the difference between rootfs and bootloader?

yes

Rootfs A/B is a feature that just added in jp4.6. While bootloader redundancy is supported for quite long.

Most of time, bl A/B is enabled by default but rootfs A/B is not, since rootfs takes too much disk space.

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If you have other specific questions, please ask. The original one was not very clear.

A/B update: feature that maintains two sets of Bootloader partitions, Slot A and Slot B, where a slot is a set of partitions that contain boot images.

Is bootloader redundancy what is meant by A/B update?

Root filesystems redundancy (“rootfs redundancy”) is a feature added on top of A/B update to provide Bootloader redundancy. It automatically maintains the same Bootloader image on both Bootloader slots, allowing the system to boot from the unused slot if the current slot is corrupted.

Rootfs redundancy is disabled by default. To enable it, see Enabling Bootloader Redundancy.

What confused me in the previous two statements is that rootfs redundancy and bootloader redundancy were used interchangeably. " Root filesystem redundancy is added to provide Bootloader redundancy", “To enable Rootfs redundancy, see Enabling Bootloader Redundancy”.

Let me double confirm with the writer of this section. Not quite sure what was his original purpose to write this.

Root filesystems redundancy (“rootfs redundancy”) is a feature added on top of A/B update to provide Bootloader redundancy.

I think the point here is you cannot enable rootfs A/B only. The bootloader A/B must be enabled along with rootfs A/B.
However, bootloader AB could be enabled when rootfs is still in disabled status.

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