[mythtv-users] Some master/slave backend advise required

Gary Buhrmaster gary.buhrmaster at gmail.com
Mon Jun 2 20:17:53 UTC 2014


On Mon, Jun 2, 2014 at 6:59 PM, Johan Van der Kolk
<johan.vanderkolk at gmail.com> wrote:
> .... master backend (which has 8TB of ZFS storage)

ZFS on Linux is not an optimal configuration.  Nor it is likely
to ever be.  The substantial differences in philosophies (and
licenses) in Linux and (the origin) Solaris regarding file
systems and buffer pools results in a less than stellar
experience.  And even in Solaris (and it various derivatives/forks)
where memory management with ZFS is much better, 4GB
would be considered very very small for 8TB of storage.

ZFS is a really great solution for many things, but it does
require a system properly sized and tuned.  You certainly
do not have it properly sized.  And ZFS tuning is still
somewhat of an art (that is why their are so many knobs
to twiddle), especially when you are trying to run it resource
constrained.

Note that ZFS on FreeBSD also has issues with the the
ARC and memory (except for some of the latest patches).

> Second part of the problem might be that the ZFS file storage
> is not fast enough. (upgrade to SSD maybe)

There can be many reasons for ZFS performance issues.
And while an all SSD array might solve them to your
satisfaction (following the "throw $$$$ at the problem" fix),
there are other potential solutions.  Whether a SSD ZIL, or
not putting all your drives in a single group (vdev) which,
in simple terms, slows down writes to single drive
performance, depends on the specifics of your system.
The naive implementation of putting all your drives into a
single raidz2 vdev sometimes surprises people with the
resulting (poor) performance.


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