Date: Thu, 27 Aug 2015 13:51:36 -0400 From: Vick Khera <vivek@khera.org> To: Marie <marieheleneka@gmail.com> Cc: Matt Churchyard <matt.churchyard@userve.net>, Marcus Reid <marcus@blazingdot.com>, "freebsd-virtualization@freebsd.org" <freebsd-virtualization@freebsd.org> Subject: Re: Options for zfs inside a VM backed by zfs on the host Message-ID: <CALd%2BdcfCuywjUSDU3JL=oHx2spNJPMtOM5RSs67f1eqLH-wtNA@mail.gmail.com> In-Reply-To: <CALXRTbeXMGCGVfQn3OuOzC3VM3si7RFyEZba=ww36FoKb_224g@mail.gmail.com> References: <CALd%2BdcfJ%2BT-f5gk_pim39BSF7nhBqHC3ab7dXgW8fH43VvvhvA@mail.gmail.com> <20150827061044.GA10221@blazingdot.com> <20150827062015.GA10272@blazingdot.com> <1a6745e27d184bb99eca7fdbdc90c8b5@SERVER.ad.usd-group.com> <CALXRTbeXMGCGVfQn3OuOzC3VM3si7RFyEZba=ww36FoKb_224g@mail.gmail.com>
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On Thu, Aug 27, 2015 at 6:10 AM, Marie <marieheleneka@gmail.com> wrote: > I've tried this in the past, and found the worst performance penalty was > with ARC disabled in guest. I tried with ARC enabled on host and guest, > only on host, only on guest. There was a significant performance penalty > with either ARC disabled. > > I'd still recommend to experiment with it on your own to see if the hit is > acceptable or not. > Thanks for all the replies. I'm going with a small-ish ARC on the VMs (about ΒΌ the allocated RAM as max, and very small amount for min) and letting the host have its substantial ARC. Since I'm running with compression=lz4 on the guest, I ended up setting compression=none on the host for the backing volumes. After some testing I found I was getting no compression on the backing volumes, so why waste the CPU overhead trying.help
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