Date: Tue, 14 Aug 2007 15:20:29 +0200 (CEST) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-chat@FreeBSD.ORG, ama@ugr.es Subject: Re: Virtualization versus jails [was Re: Creating and copying jail ?images] Message-ID: <200708141320.l7EDKTxJ085964@lurza.secnetix.de> In-Reply-To: <20070814100440.GA13819@darwin.ugr.es>
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Angel Martin Alganza wrote: > Supposing one doesn't need to run different operating systems or even > different kernel versions of the same OS, are there any advantages of > virtualization (Xen) over jails? Both can be copied, moved around, > switched on/off, replaced with almos 0 downtime, etc. What do you > think about that? Jails don't give you a perfect separation. Jails still run under the same kernel as the host system, and if there's a bug somewhere, you're out of luck. You can also run into various kinds of resource starvation with jails, i.e. jails can use up shared resources. All of that isn't possible (or at least to a much smaller degree) with virtualization solutions (xen, qemu, vmware, whatever), because they run the guest systems in a virtual machine with their own kernel and resources. Having said that, jails are still a good solution for a number of things, depending on your needs, and they do have advantages, too. For example, in general jails have less overhead than virtual machines, and sometimes you want sharing of certain resources, e.g. RAM. That's why you can run thousands of jails on a single server, but when you need virtual machines, you can usually do only a dozen or two. There's also a third possibility: Virtual kernels, such as the vkernel feature of DragonFly BSD. It does not emulate a virtual machine, but allows processes to be run under a completely separate kernel (which itself is running as a process under the "real" kernel). Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M. Handelsregister: Registergericht Muenchen, HRA 74606, Geschäftsfuehrung: secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün- chen, HRB 125758, Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart FreeBSD-Dienstleistungen, -Produkte und mehr: http://www.secnetix.de/bsd One Unix to rule them all, One Resolver to find them, One IP to bring them all and in the zone to bind them.
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