I currently download once and upgrade three different systems by
rsync-ing the cache.
Do I understand that this will no longer be supported or work?
That's an interesting question. Is sharing the cache directory from a single host
intended to be shared like this? I am guessing no, but it may still be common.
It should still work, with two caveats:
1. The files in the cache will be bigger, so a simple rsync will involve more I/O, and the
destination filesystem will also need more space and I/O time.
2. The systems must be the same endianness (The transcoded format doesn't bother with
network order, because it's not intended to be shared)
3. The page size must be the same for reflinking to work: This is actually worked out when
the filesystem is created, and defaults to the system page size, and if not the same as
the current page size, the filesystem isn't even guaranteed to mount (see --sectorsize
option in mkfs.btrfs man page).
In reality you're quite unlikely to share packages unless the architecture were the
same, which would steer both endianness and page size to the same value. That said,
I'm aware that aarch64 can be flexible in both ways. I'm covering my bases with my
statement: I have thought about it, and don't think I'm in any position to make
promises.
For this proposal: we're talking about shipping the code that would allow this to be
turned on. We're not talking about enabling it by default. We can't until we have
good answers to questions like this.
Thanks, Matthew.