Does this disk/filesystem layout look sane to you?

George Hartzell hartzell at
Mon Jun 15 15:47:46 UTC 2009

Freddie Cash writes:
 > On Sun, Jun 14, 2009 at 9:17 AM, Dan Naumov <dan.naumov at> 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: 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?


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