RFC: Suggesting ZFS "best practices" in FreeBSD

[Peter Jeremy]

On 2013-Jan-22 17:27:13 -0800, Michael DeMan <freebsd at deman.com> wrote:
>- probably there are enough people even though it seems pretty obvious in a couple more years nobody will have 32-bit or less than 8GB RAM?

FreeBSD goes into an awful lot of embedded devices which are unlikely
to transition off 32-bit or have more than a few hundred MB RAM for
the foreseeable future.  Definitely, the PC world is going that way -
but it's heavily driven by Microsoft and it's quite likely that the
next version of Windows won't fit into 32-bits.

>I could be disinformed here, but my understanding) is best practice is to use gpart + gnop to:
>#1.  Ensure proper alignment for 4K sector drives - the latest western digitals still report as 512.

Recent versions of ZFS allow you to specify ashift=12 without needing
gnop.  And in any case, gnop is only needed when you initialise the
pool.  Once the initial ashift value is set, it can't be changed.
(And I'd be interested in knowing how well a SSD ZIL compensates for
having an ashift=9 pool on 4K sector disks).

>#2.  Ensure a little extra space is left on the drive since if the whole drive is used, a replacement may be a tiny bit smaller and will not work.

As someone else has mentioned, recent ZFS allows some slop here.  But
I still think it's worthwhile carving out some space to allow for a
marginally smaller replacement disk.

>#3.  Label the disks so you know what is what.
With a paper label and a pen.

>ZFS GENERAL BEST PRACTICES - address the regular ZFS stuff here 
>- why the ZIL is a good thing even you think it kills your NFS performance
>- no vdevs > 8 disks, raidz1 best with 5 disks, raidz2 best with 6 disks, etc.
>- striping over raidz1/raidz2 pools
>- striping over mirrors
>- etc...

Most of this can be pointers to generic ZFS documentation.  Which brings
up another point - the documentation should make it clear whether a
particular hint is FreeBSD-specific or generic across all ZFS platforms.
And what "generic" ZFS hints are unnecessary on FreeBSD.

-- 
Peter Jeremy
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