ZFS root on MB Intel S3420GP

[Daniel Kalchev]

On 17.04.11 21:54, Jeremy Chadwick wrote:
> I don't recommend enabling ahci.ko after the OS has already been
> installed on an adX disk, simply because I believe the combination of
> GEOM+CAM+ahci may show different geometry details than GEOM+ata would.
>
With the disclaimer that I haven't studied all code to confirm this, but 
adX and adaX (with ahci.ko) have always played the same for me - 
geometry wise. I believe the translation is always 1:1. At least on 
modern SATA drives -- olderdrives from the transitional epoch of 
different CHS, LBA etc experiments might behave differently.

Migration from gmirror to zfs(root) is trivial. Having only two 
gmirror-ed disks, you could replace that with ZFS mirror. Having 4-way 
gmirror can let you do a 4-disk ZFS migration (raidz1 or raidz2).

I tend to do all of my new systems with ZFS on root. Probably because I 
no longer have to do systems that run with few MB of RAM :) - the I 
would use UFS alwats.

One nice feature of ZFS I have discovered is with USB flash media. You 
are not typically supposed to write much to that media, but using UFS on 
USB sticks is awful. On contrary, when used with ZFS, the USB sticks 
behave much differently, because ZFS will group writes and not do silly 
things like issue lots of 512 byte writes. So, you may have complete 
development system on an USB stick, or a pair of these. The only real 
trouble with USB stisks is that some motherboards behave unpredictable 
as to boot order, but this is improving.

My recent "install procedure" never used the FreeBSD release media. 
Instead, I have created myself USB stick distribution media (can work 
with CD/DVD as well, or over diskless boot), using a procedure like this:

- on an up to date FreeBSD system, do make buildworld; make buildkernel
- insert the USB stick, create filesystem. UFS or ZFS, doesn't matter
- make installworld, make installkernel, make distribution to the 
mounted USB stick
- fix fstab and loader.conf on the USB stick
(optional)
- copy over src and ports tree ro the USB stick
- do in place rebuild/reinstall of the world, kernel and any packages 
you may need
(end optional)
- put the USB stick in my pocket

Next time, I need to install a server on site, take the USB stick out of 
my pocket, plug it in one of the USB ports, boot the server, run small 
script (similar to that in the root-on-zfs guides), create ZFS on root 
and am done with it. I would use either pair of USB sticks for that, a 
separate set of (two) disk drives, or 'all' of the system's drives for 
this install, depending on the systems intended usage and hardware 
configuration. Typically on a multi-bay system I would do the root on a 
separate set of disks/USB flash in order to simplify documentation and 
operator training.

If the system needs to be installed remotely, I would typically use rKVM 
(most rackmount-intended motherboards have this functionality), 
attaching either the prepared USB stick or it's image are virtual media 
and booting over that the new system.

Many of these things can be done differently of course, it will depend 
on circumstances, but I hope the general idea is useful.

Jeremy, one of the reasons I switched many systems to "pure ZFS" was 
related to the memory allocation troubles between USF and ZFS we 
observed for quite long time. Having pure ZFS system eliminates these 
issues completely. I do have still few mixed systems - only laziness and 
lack of (down)time prevented me from switching these to pure-ZFS too. My 
rationale is that if something breaks, it is likely it will break with 
or without ZFS on root. In either case, I would have to load FreeBSD 
from other media. So it does not matter from where you boot the system.

One final note, on ZFS pool naming. I would traditionally name my 
root-on-zfs pool 'system'. However, this makes it difficult and error 
prone to create new zpools. Therefore, I have zpool of 'boot' for my 
install USB sticks and also have addopted the practice of naming the 
root pool after it's system's name. For example 'hostABCroot' or 
'hostABCsystem'. This has never been an issue with UFS, until filesystem 
labels appeared and still not that many people use these. With ZFS, you 
cannot escape.

Daniel