Date: Thu, 27 Aug 2015 10:46:43 -0400 From: Allan Jude <allanjude@freebsd.org> To: freebsd-virtualization@freebsd.org Subject: Re: Options for zfs inside a VM backed by zfs on the host Message-ID: <55DF22D3.1040302@freebsd.org> In-Reply-To: <20150827061044.GA10221@blazingdot.com> References: <CALd%2BdcfJ%2BT-f5gk_pim39BSF7nhBqHC3ab7dXgW8fH43VvvhvA@mail.gmail.com> <20150827061044.GA10221@blazingdot.com>
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This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --oaFB5gvVXRR7m9QmbFDpWecE7MhHSsq3P Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 2015-08-27 02:10, Marcus Reid wrote: > On Wed, Aug 26, 2015 at 05:25:52PM -0400, Vick Khera wrote: >> I'm running FreeBSD inside a VM that is providing the virtual disks ba= cked >> by several ZFS zvols on the host. I want to run ZFS on the VM itself t= oo >> for simplified management and backup purposes. >> >> The question I have is on the VM guest, do I really need to run a raid= -z or >> mirror or can I just use a single virtual disk (or even a stripe)? Giv= en >> that the underlying storage for the virtual disk is a zvol on a raid-z= >> there should not really be too much worry for data corruption, I would= >> think. It would be equivalent to using a hardware raid for each compon= ent >> of my zfs pool. >> >> Opinions? Preferably well-reasoned ones. :) >=20 > This is a frustrating situation, because none of the options that I can= > think of look particularly appealing. Single-vdev pools would be the > best option, your redundancy is already taken care of by the host's > pool. The overhead of checksumming, etc. twice is probably not super > bad. However, having the ARC eating up lots of memory twice seems > pretty bletcherous. You can probably do some tuning to reduce that, bu= t > I never liked tuning the ARC much. >=20 > All the nice features ZFS brings to the table is hard to give up once > you get used to having them around, so I understand your quandry. >=20 > Marcus > _______________________________________________ > freebsd-virtualization@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-virtualization > To unsubscribe, send any mail to "freebsd-virtualization-unsubscribe@fr= eebsd.org" >=20 You can just: zfs set primarycache=3Dmetadata poolname And it will only cache metadata in the ARC inside the VM, and avoid caching data blocks, which will be cached outside the VM. You could even turn the primarycache off entirely. --=20 Allan Jude --oaFB5gvVXRR7m9QmbFDpWecE7MhHSsq3P Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (MingW32) iQIcBAEBAgAGBQJV3yLjAAoJEBmVNT4SmAt+k/YP/3aQShmax1KoeIpGIXYODdzs 6/b2Gz1R/wFjYWrXIh5RrN3U4h+Ov6hv19MXG+561I/yaqaB9rH6En2hJjOhrI7g iqPDa4sb/LwpeNWRbfl1K00QjCmE8BlcdrACS5qbUO2J+aVItree23LNKrKfZz5a d8Fem4oLihaBVyyTjEqLIBXDoGJdkD5LdHMC2E/iqqN/tRa+5xBa7p7kpf1LWXGV jicFcgxvExgDP1wvmMQmNzje4Gpfc8jDF7MYm/BCzhsODXfMy4ckszkObv5VyljT pnloZ80WXyrOOH5OkooBu8BtDOM915rew43I7HmfinG7kpdPklInCwE//3yos2gH x2B39ohdcek7FRLRl70uUIUzBqGKAYVuWmUrbUcD7oSKICQKboofE1y6bW3xX0z4 IKIk0snhjhc7aUx7EADznYrnzEemxDPrV147sMCQVbI+S1zIvcSuf4YQoq98vIv0 URxCljdd9BkymlwK0zKMo2aA3bI214jmBy0wkJUPtbI070B+meKDTqMo5517gQal 94THEX8rVCHKhDKYwIbRxA+EAXWUFh8FAGxxf2NjpZe/Zs2PPETaJ6WAAYT17vce RtX60kDKkuDrTJ7dktKapmtWHK2hvPiBYkhGgBbf9weBear5UV+IXsX/r9HAXIny rbfP8UQA4wNx3oKFJG1a =V8ux -----END PGP SIGNATURE----- --oaFB5gvVXRR7m9QmbFDpWecE7MhHSsq3P--
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