Mmm, I can't disagree if that's what the code says .. however turning off the cache completely in the GUI does "seem" to make quite a *dramatic* difference to the VM performance, whereas setting the sharable flag seems to have no performance impact at all .. (when using writethrough ...) ???
-- Gareth Bult “The odds of hitting your target go up dramatically when you aim at it.” See the status of my current project at http://vdc-store.com ----- Original Message ----- From: "Javier Fontan" <jfon...@opennebula.org> To: "Gareth Bult" <gar...@linux.co.uk> Cc: "Stefan Kooman" <ste...@bit.nl>, users@lists.opennebula.org Sent: Thursday, 30 January, 2014 2:48:15 PM Subject: Re: [one-users] Setting the "SHAREABLE" attribute I'll investigate a bit more on this issue but from the qemu driver code it seems that cache is disabled with shareable flag. On Thu, Jan 30, 2014 at 4:07 PM, Gareth Bult <gar...@linux.co.uk> wrote: > Mmm, there has been some discussion around this .. > > Technically using cache=writeback "should" be safe for migration. > (which is the method I use) > > So .. I need "cache=writeback" and "sharable" for migration to happen. > (the performance hit with cache=off is an unacceptable performance hit, at > least for me ..) > > From the QEMU lists, 2012; > "In short, if you're using a recent kernel with ext3 or ext4, cache=writeback > is absolutely safe. If you're using an older version of ext3, cache=writeback > is still safe but ext3 itself isn't. cache=writeback can make the situation > worse." > > ... > > > -- > > Gareth Bult > "The odds of hitting your target go up dramatically when you aim at it." > See the status of my current project at http://vdc-store.com > > > ----- Original Message ----- > From: "Stefan Kooman" <ste...@bit.nl> > To: "Javier Fontan" <jfon...@opennebula.org> > Cc: "Gareth Bult" <gar...@linux.co.uk>, users@lists.opennebula.org > Sent: Thursday, 30 January, 2014 2:38:23 PM > Subject: Re: [one-users] Setting the "SHAREABLE" attribute > > Quoting Javier Fontan (jfon...@opennebula.org): >> I've been digging a bit more in the shareable issue and it seems that >> setting "shareable" to a disk just disables cache in qemu/kvm[1]: >> >> --8<------ >> 4158 virBufferAsprintf(&opt, ",cache=%s", mode); >> 4159 } else if (disk->shared && !disk->readonly) { >> 4160 virBufferAddLit(&opt, ",cache=off"); >> 4161 } >> ------>8-- >> >> Isn't it enough to disable cache for disks that can be migrated? > Yes it is, at least in our environment (Ubuntu 13.10). Cache has to be > off (to avoid data loss while migrating vm). > > /etc/one/vmm_exec/vmm_exec_kvm.conf: > > DISK = [ driver = "raw" , cache = "none", io = "native"] > > Gr. Stefan > > > -- > | BIT BV http://www.bit.nl/ Kamer van Koophandel 09090351 > | GPG: 0xD14839C6 +31 318 648 688 / i...@bit.nl -- Javier Fontán Muiños Developer OpenNebula - The Open Source Toolkit for Data Center Virtualization www.OpenNebula.org | @OpenNebula | github.com/jfontan _______________________________________________ Users mailing list Users@lists.opennebula.org http://lists.opennebula.org/listinfo.cgi/users-opennebula.org