Boot partition size

[Aristedes Maniatis]

Thanks for your reply Warner,


On 29/1/17 3:50pm, Warner Losh wrote:
> Unless you are running on tiny disks, you should use 512kB for maximum
> future proofing. Given the bloat that's happened in boot1/boot2 over
> the years, this is the only sensible default.


Then you ('you' in the very generic FreeBSD committers with permission sense) should get the wiki changed (link in my previous email) to give better advice. The advice of 128kB seems bad. More people will be hurt.

 
>> 2. Is there any possible short term future where ZFS volumes can be shrunk, or will I be replacing every hard disk (or rebuilding the machine from scratch)?
> Not easily. However, there's several options available to you: (1) not
> upgrading the boot partition

That seems contrary to the advice that zpool provides when you upgrade a pool. It specifically tells you that it is really important to upgrade the boot partition. But it doesn't tell you this is impossible due to space requirements *before* you upgrade the pool.

Is your suggestion to continue upgrading the OS, but never upgrade the pool?


>  (2) shrinking a swap partition to snag
> some space 

Yes, except I put my swap into a zvol. I did this when I lost a disk once with a dedicated swap partition and that caused the system to crash. So I realised that dedicated swap was a really bad idea and I needed to choose between zvol and gmirror. I chose zvol to avoid having one more thing to check and worry about.


> (3) putting a larger boot partition at the 'end' of the
> disk where there's usually runt sectors due to how gpart (bogusly
> imho, but I've not been successful at advocating this viewpoint)
> rounds. There's up to an entire cylinder at the end (though LBAs make
> CHS bogus), which might be useful. It's also possible to move the
> start of the boot partition to a smaller LBA, which gives us more than
> the 44k we currently have. We may also be able to write a smaller GPT
> area if we use only a couple of partitions on the disk.


I read that the boot partition had to be the first partition on disk. Is that wrong?

> In this case, there's no compelling
> reason to upgrade the boot blocks that I can see... A quick look at
> freebsd-update shows no calls to gpart or dd, which is necessary to
> change them.

But if we are using new ZFS code, and we upgrade the zpool, might that not require new boot code to be able to boot the system?

I've already got one system I upgraded to FreeBSD 11, upgraded the pool once everything looked good, and now I cannot upgrade the boot code. I don't want to restart the machine... ever. That's possibly unrealistic, although I could boot from USB in an emergency I guess.


Ari Maniatis



-- 
-------------------------->
Aristedes Maniatis
CEO, ish
https://www.ish.com.au
GPG fingerprint CBFB 84B4 738D 4E87 5E5C  5EFA EF6A 7D2E 3E49 102A

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