Does this disk/filesystem layout look sane to you?

[Freddie Cash]

On Mon, Jun 15, 2009 at 8:47 AM, George Hartzell <hartzell at alerce.com>wrote:

> Freddie Cash writes:
>  > On Sun, Jun 14, 2009 at 9:17 AM, Dan Naumov <dan.naumov at gmail.com>
> wrote:
>  >
>  > > I just wanted to have an extra pair (or a dozen) of eyes look this
>  > > configuration over before I commit to it (tested it in VMWare just in
>  > > case, it works, so I am considering doing this on real hardware soon).
>  > > I drew a nice diagram: http://www.pastebin.ca/1460089 Since it doesnt
>  > > show on the diagram, let me clarify that the geom mirror consumers as
>  > > well as the vdevz for ZFS RAIDZ are going to be partitions (raw disk
>  > > => full disk slice => swap partition | mirror provider partition | zfs
>  > > vdev partition | unused.
>  >
>  >
>  > I don't know for sure if it's the same on FreeBSD, but on Solaris, ZFS
> will
>  > disable the onboard disk cache if the vdevs are not whole disks.  IOW,
> if
>  > you use slices, partitions, or files, the onboard disk cache is
> disabled.
>  > This can lead to poor write performance.
>  >
>  > Unless you can use one of the ZFS-on-root facilities, I'd look into
> getting
>  > a couple of CompactFlash or USB sticks to use for the gmirror for / and
> /usr
>  > (put the rest on ZFS).  Then you can dedicate the entirety of all 5
> drives
>  > to ZFS.
>
> Even if you use do a bootable ZFS on root, you'll end up with a couple
> of gpt partitions (boot code, swap, then root) and therefor
> constructing your ZFS file system from a partition.
>
> Pawel said, back on April 6, 2007,
>
>   "We support cache flushing operations on any GEOM provider (disk,
>    partition, slice, anything disk-like), so bascially currently I
>    treat everything as a whole disk [...]"
>
> Does anyone know for sure if we disable caching for partitions?
>

Going back through some old threads, it seems that I was mistaken, and it's
only on Solaris that disk cache is disabled for vdevs created from
partitions.  3 cheers for GEOM.  :)

-- 
Freddie Cash
fjwcash at gmail.com