From owner-freebsd-virtualization@freebsd.org Thu Aug 27 09:42:28 2015 Return-Path: Delivered-To: freebsd-virtualization@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 2E4749C4CE3 for ; Thu, 27 Aug 2015 09:42:28 +0000 (UTC) (envelope-from matt.churchyard@userve.net) Received: from smtp-outbound.userve.net (smtp-outbound.userve.net [217.196.1.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.userve.net", Issuer "Go Daddy Secure Certificate Authority - G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id D3ACF791 for ; Thu, 27 Aug 2015 09:42:27 +0000 (UTC) (envelope-from matt.churchyard@userve.net) Received: from owa.usd-group.com (owa.usd-group.com [217.196.1.2]) by smtp-outbound.userve.net (8.15.1/8.15.1) with ESMTPS id t7R9VuHU050816 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=FAIL); Thu, 27 Aug 2015 10:31:56 +0100 (BST) (envelope-from matt.churchyard@userve.net) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=userve.net; s=201508; t=1440667919; bh=Hjul30xjdPl/DzeFkEBcXJBfmRfhhk4FqVmhHBwZvxw=; h=From:To:CC:Subject:Date:References:In-Reply-To; b=gpFYCcO8JScdw1pMGR/uR4XvzD7YyqVjAHT8aqgTQwupnpY44cHAnU90KLvn9kPJf 0iHTU6jEGJOZoqX6ZWB9tHOWDimRQLLCupT2u3lLCQY/+qI/AlqzMfeOLrd1OI5aYM sI5ekuwnlLF8nmiZcI0BHUpyEh5ndxzHHo20ZPvU= Received: from SERVER.ad.usd-group.com (192.168.0.1) by SERVER.ad.usd-group.com (192.168.0.1) with Microsoft SMTP Server (TLS) id 15.0.847.32; Thu, 27 Aug 2015 10:31:50 +0100 Received: from SERVER.ad.usd-group.com ([fe80::b19d:892a:6fc7:1c9]) by SERVER.ad.usd-group.com ([fe80::b19d:892a:6fc7:1c9%12]) with mapi id 15.00.0847.030; Thu, 27 Aug 2015 10:31:50 +0100 From: Matt Churchyard To: Marcus Reid , Vick Khera CC: "freebsd-virtualization@freebsd.org" Subject: RE: Options for zfs inside a VM backed by zfs on the host Thread-Topic: Options for zfs inside a VM backed by zfs on the host Thread-Index: AQHQ4EXX3kz9NYJz1USC2V7pGvPRBp4fTOcAgAACqYCAAEI88A== Date: Thu, 27 Aug 2015 09:31:50 +0000 Message-ID: <1a6745e27d184bb99eca7fdbdc90c8b5@SERVER.ad.usd-group.com> References: <20150827061044.GA10221@blazingdot.com> <20150827062015.GA10272@blazingdot.com> In-Reply-To: <20150827062015.GA10272@blazingdot.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [192.168.0.10] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-BeenThere: freebsd-virtualization@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Discussion of various virtualization techniques FreeBSD supports." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 27 Aug 2015 09:42:28 -0000 > On Wed, Aug 26, 2015 at 11:10:44PM -0700, Marcus Reid wrote: > On Wed, Aug 26, 2015 at 05:25:52PM -0400, Vick Khera wrote: > > > Opinions? Preferably well-reasoned ones. :) > > >=20 > > However, having the ARC eating up lots of memory twice seems pretty=20 > > bletcherous. You can probably do some tuning to reduce that, but I=20 > > never liked tuning the ARC much. > I just realized that you can turn primarycache off per-dataset. Does it = make more sense to turn primarycache=3Dnone on the zvol on the host, or > o= n the datasets in the vm? I'm thinking on the host, but it might be worth = experimenting. I'd be very wary of disabling ARC on the main host, it can have pretty seri= ous side effects. It could possibly be useful in the guest though, as data = should be cached already by ARC on the host, you're just going through an e= xtra step of reading through the virtual disk driver, and into host ARC, in= stead of directly from the guest memory. Would need testing to know what pe= rformance was like and if there are any side effects. I do agree that it doesn't seem unnecessary to have any redundancy in the g= uest if the host pool is redundant. Save for any glaring bugs in the virtua= l disk emulation, you wouldn't expect to get errors on the guest pool if th= e host pool is already checksumming the data. It's also worth testing with guest ARC enabled but just limited to a fairly= small size, so you're not disabling it entirely, but doing at little doubl= e-caching as possible. ZFS features seems perfect for virtual hosts, although it's not ideal that = you have to give up a big chunk of host RAM for ARC. You may also find that= you need to limit host ARC, then only use "MAX_RAM - MY_ARC_LIMIT" for gue= sts. Otherwise you'll have ZFS and VMs fighting for memory and enough of us= have seen what shouldn't, but unfortunately does happen in that situation. Matt - > Marcus > _______________________________________________ > freebsd-virtualization@freebsd.org mailing list https://lists.freebsd.org= /mailman/listinfo/freebsd-virtualization > To unsubscribe, send any mail to "freebsd-virtualization-unsubscribe@free= bsd.org"