Date: Tue, 19 Mar 2019 09:06:11 +0100 From: "Patrick M. Hausen" <hausen@punkt.de> To: Victor Sudakov <vas@mpeks.tomsk.su> Cc: freebsd-virtualization@freebsd.org Subject: Re: bhyve and vfs.zfs.arc_max, and zfs tuning for a hypervisor Message-ID: <AA997A20-4EBF-46DF-A517-FD2072682545@punkt.de> In-Reply-To: <20190319024638.GA8193@admin.sibptus.ru> References: <20190319024638.GA8193@admin.sibptus.ru>
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Hi! > Am 19.03.2019 um 03:46 schrieb Victor Sudakov <vas@mpeks.tomsk.su>: > 1. Does ARC actually cache zfs volumes (not files/datasets)? Yes it does. > 2. If ARC does cache volumes, does this cache make sense on a = hypervisor, > because guest OSes will probably have their own disk cache anyway. IMHO not much, because the guest OS is relying on the fact that when it writes it=E2=80=99s own cached data out to =E2=80=9Edisk=E2=80=9C, it = will be committed to stable storage. > 3. Would it make sense to limit vfs.zfs.arc_max to 1/8 or even less of > total RAM, so that most RAM is available to guest machines? Yes if you build your own solution on plain FreeBSD. No if you are = running FreeNAS which already tries to autotune the ARC size according to the memory committed to VMs. > 4. What other zfs tuning measures can you suggest for a bhyve > hypervisor? e.g. zfs set sync=3Dalways zfs/vm if zfs/vm is the dataset under which you create the ZVOLs for your = emulated disks. I=E2=80=99m using this for all my VM =E2=80=9Edisks=E2=80=9C and have = added a 16 GB SLOG device to my spinning disk pool - seems to work great. This is on a home = system. Our new data centre systems feature all NVME SSDs and no spinning rust. So no need for a separate SLOG. HTH, Patrick --=20 punkt.de GmbH Internet - Dienstleistungen - Beratung Kaiserallee 13a Tel.: 0721 9109-0 Fax: -100 76133 Karlsruhe info@punkt.de http://punkt.de AG Mannheim 108285 Gf: Juergen Egeling
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