Date: Sun, 29 Jan 2017 16:43:37 +1100 From: Aristedes Maniatis <ari@ish.com.au> To: Warner Losh <imp@bsdimp.com> Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: Boot partition size Message-ID: <54f66195-2929-ef8c-ac53-deaec574c182@ish.com.au> In-Reply-To: <CANCZdfrbKiH448k_6AWVaGS8TT3E109yW1tyLdQXJpGchvzErw@mail.gmail.com> References: <a4cab85a-5e79-c7c1-fbb7-d9cf83cbf556@ish.com.au> <CANCZdfrbKiH448k_6AWVaGS8TT3E109yW1tyLdQXJpGchvzErw@mail.gmail.com>
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From: Aristedes Maniatis <ari@ish.com.au>
To: Warner Losh <imp@bsdimp.com>
Cc: freebsd-stable <freebsd-stable@freebsd.org>
Message-ID: <54f66195-2929-ef8c-ac53-deaec574c182@ish.com.au>
Subject: Re: Boot partition size
References: <a4cab85a-5e79-c7c1-fbb7-d9cf83cbf556@ish.com.au>
<CANCZdfrbKiH448k_6AWVaGS8TT3E109yW1tyLdQXJpGchvzErw@mail.gmail.com>
In-Reply-To: <CANCZdfrbKiH448k_6AWVaGS8TT3E109yW1tyLdQXJpGchvzErw@mail.gmail.com>
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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 se=
nse) should get the wiki changed (link in my previous email) to give bett=
er advice. The advice of 128kB seems bad. More people will be hurt.
=20
>> 2. Is there any possible short term future where ZFS volumes can be sh=
runk, or will I be replacing every hard disk (or rebuilding the machine f=
rom 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 th=
e 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 po=
ol?
> (2) shrinking a swap partition to snag
> some space=20
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 choo=
se 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 no=
t 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 o=
nce everything looked good, and now I cannot upgrade the boot code. I don=
't want to restart the machine... ever. That's possibly unrealistic, alth=
ough I could boot from USB in an emergency I guess.
Ari Maniatis
--=20
-------------------------->
Aristedes Maniatis
CEO, ish
https://www.ish.com.au
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