Date: Sun, 29 Jan 2017 19:20:49 -0800 From: Freddie Cash <fjwcash@gmail.com> To: Gary Palmer <gpalmer@freebsd.org> Cc: FreeBSD Stable <freebsd-stable@freebsd.org>, Aristedes Maniatis <ari@ish.com.au> Subject: Re: Boot partition size Message-ID: <CAOjFWZ6WRQ5i4OP5ZK89RxM1YpMbVp%2BcOHCSvUyUx0etizUmog@mail.gmail.com> In-Reply-To: <20170129141244.GA63867@in-addr.com> References: <a4cab85a-5e79-c7c1-fbb7-d9cf83cbf556@ish.com.au> <20170129141244.GA63867@in-addr.com>
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On Jan 29, 2017 6:13 AM, "Gary Palmer" <gpalmer@freebsd.org> wrote: On Sun, Jan 29, 2017 at 03:15:19PM +1100, Aristedes Maniatis wrote: > As recently as last October, the best official advice was to make a 64kB boot partition. > > https://wiki.freebsd.org/action/diff/RootOnZFS/ GPTZFSBoot/Mirror?action=diff&rev1=16&rev2=17 > > > Now that turns out to be absolutely terrible advice and some people (like me) have dozens of machines that will never be upgradable to FreeBSD 11 or higher. It looks like there is no reasonable method of upgrade that doesn't involve replacing every hard disk on every machine (that's hundred of disks) with larger models. I use a zvol for swap, so I can't make swap smaller to solve the problem. > > I started with FreeBSD 4.1 and in 16 years... sigh... > > The ashift pain some years ago was also caused by FreeBSD default recommendations and settings not anticipating future needs quickly enough. But this mess now is completely self-inflicted foot shooting. > > > 1. Why is the recommendation now 128kB and not much much higher? When that limit is broken in a couple of years, will there be another round of annoyed users? Is someone concerned that ZFS users are running hard disks over under 500Mb and need to save space? Surely the recommendation should be 512kB? > > 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)? It is highly unlikely that ZFS volumes will be able to be reduced in size even in the long term. I believe that requires a piece of work that has been rated as very difficult to do without violating layering policies inside the ZFS code. The alternative is, assuming you have a pool with redundancy (e.g. mirror) is to do a backup, drop one half of the mirror, create a new pool on the now unused disk, zfs send | zfs receive, boot from the new pool and then drop the old pool and add the disk to the mirror You can also format a larger drive with the correct partition sizes, and do a "zpool replace" (for raidz vdevs) or "zpool detach/attach" (for mirror vdevs). No send/recv required. And, you may be able to do that on the existing disks, as ZFS now leaves a MB or two of "slack space" at the end of the device used in the vdev. This allows for using drives/partitions that are the same size in MB but have different numbers of sectors. This was an issue on the early ZFS days. So, you may be able to resize the freebsd-zfs partition by a handful of KB without actually changing the size of the vdev. Cheers, Freddie
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