Date: Wed, 20 Mar 2019 08:52:36 +0700 From: Victor Sudakov <vas@mpeks.tomsk.su> To: freebsd-virtualization@freebsd.org Subject: Re: bhyve and vfs.zfs.arc_max, and zfs tuning for a hypervisor Message-ID: <20190320015236.GA35511@admin.sibptus.ru> In-Reply-To: <AA997A20-4EBF-46DF-A517-FD2072682545@punkt.de> References: <20190319024638.GA8193@admin.sibptus.ru> <AA997A20-4EBF-46DF-A517-FD2072682545@punkt.de>
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[-- Attachment #1 --] Patrick M. Hausen wrote: > > > 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’s own cached data out to „disk“, it will be committed to > stable storage. This is an important point. > > 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=always zfs/vm > > if zfs/vm is the dataset under which you create the ZVOLs for your emulated > disks. Well, bhyve already has an option for this: The block-device-options are: nocache Open the file with O_DIRECT. direct Open the file using O_SYNC. ro Force the file to be opened read-only. I think something like "-s 4:0,virtio-blk,/dev/zvol/zroot/vm/mail/disk0,direct" would do the same? > > I’m using this for all my VM „disks“ and have added a 16 GB SLOG device > to my spinning disk pool - seems to work great. This is on a home system. Is SLOG also used by zfs volumes? -- Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/ [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- iQEbBAEBAgAGBQJckZzkAAoJEA2k8lmbXsY0uukH+JC3YmtDNjPduavG8UcnK1Dy nMPQwavDdOyKK8v37n1K11ftUbdEOaHC+IWrrszuUxc3Ui/hPG6K3FAaLtLtwllp 6p+64AJ9w9t/nIoMfIGJfmU1BMQuE0JeXcJCaohoDXvyMfCxXApdxlK3iRRYa97T 8ch7Bc+f77cYuwvJkj0eW2pSmANObTsj5kcCLDhnWX9EuBoDpE1rmhfB1R1zxJaa 5PYpNChx8tqyb+O/Usex6pnZ9B7pKzO4lf4mDB13yg6ysWYnCGhECi54yZbE146h OMaJsLpE1DxOe3aOCGsx19o5Fi+/mXb4qm1nwWTE5Jv+/zvtlVxjla+UySB0Dg== =dqCO -----END PGP SIGNATURE-----help
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