Date: Tue, 24 Mar 2015 07:53:50 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Jason Birch <jbirch@jbirch.net> Cc: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org> Subject: Re: Possible (or smart) to put freebsd-boot on USB stick for root-on-ZFS? Message-ID: <alpine.BSF.2.20.1503240735350.21722@wonkity.com> In-Reply-To: <CAA=KUhvYfhJ9i_CU6Lhni0EB03zjPMBpBHOHLJ92THVs2owZxw@mail.gmail.com> References: <CAA=KUhvYfhJ9i_CU6Lhni0EB03zjPMBpBHOHLJ92THVs2owZxw@mail.gmail.com>
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On Tue, 24 Mar 2015, Jason Birch wrote: > Hey there, > > I'm looking at a relatively old resource > (https://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/9.0-RELEASE) about how > to run root on ZFS for 9.0, and I noticed the section on installing > the boot section to all drives that make up the root. In my setup, > I'll only be mirroring two SSDs on 10.1, but it made me consider the > possibility of having the freebsd-boot partition on a USB stick rather > than on each drive itself for basically the following reason: > > Should an SSD die, I'd need to say "boot from this other device" to > get my system back up and running, do the original partitioning magic > on the replacement device, get that back into the vdev... Should the > USB stick die, I'd need to simply replace it with one that had the > same image (that is, only the boot partition), and `zpool replace` a > blank device (I won't have a swap partition). > > However, I can think of some downsides as well - namely that the USB > stick is probably more likely to die than the SSDs, and that the image > on the USB stick will change over time (This gets mounted as /boot? or > am I mistaken here... This would plague the freebsd-boot on the SSDs > as well, with drift...) The freebsd-boot partition does not have a filesystem. The only thing in it is the binary bootcode, like gptzfsboot(8). > Am I misinterpreting the point of freebsd-boot? Does /boot actually > end up living on the ZFS mount, and freebsd-boot just contains enough > information to read the kernel and other goodies required to bring up > a full system from a ZFS dataset? That is correct. > Is my thought to use a USB stick for this partition a little thick or > actually worth trying out? The bootcode changes rarely, and is usually not a problem. Having a separate, duplicate /boot is sometimes done for geli(8). It's kind of a pain, because changes must be made in two places. For a mirror with the OS on it, I'd put a freebsd-boot partition on each drive, manually install the bootcode to each, and call it good.
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