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This is where it actually confuses me. According to the ceph document (http://ceph.com/docs/master/rbd/qemu-rbd/),
"QEMU’s cache settings override Ceph’s default settings (i.e., settings that are not explicitly set in the Ceph configuration file). If you explicitly set RBD Cache settings in your Ceph configuration file, your Ceph settings override the QEMU cache settings. If you set cache settings on the QEMU command line, the QEMU command line settings override the Ceph configuration file settings." If I set the qemu caching parameter in nova.conf by, disk_cachemodes="network=writeback" This would give me "cache=writeback" in the qemu cmd argument for rbd device when VM is created. According to the ceph doc above, It would be equivalent to setting of "rbd_cache = true". Since I am not specifying any other rbd parameters (e.g, rbd_cache_size, etc) in the qemu command line (or it can't be done anyway according to the blueprint), those should be default to what I have set in ceph.conf? Or my understanding of the ceph document is completely off-base? --weiguo P.S., My original question is actually regarding how the "if=" parameter impacts the rbd performance, which is not directly related to rbd caching configuration. From: sebastien.han@xxxxxxxxxxxx Date: Thu, 13 Jun 2013 15:59:06 +0200 To: Oliver.Francke@xxxxxxxx CC: ceph-users@xxxxxxxxxxxxxx; wsun2@xxxxxxxxxxx Subject: Re: QEMU -drive setting (if=none) for rbd OpenStack doesn't know how to set different caching options for attached block device. See the following blueprint, https://blueprints.launchpad.net/nova/+spec/enable-rbd-tuning-options This might be implemented for Havana. Cheers. –––– Sébastien Han Cloud Engineer "Always give 100%. Unless you're giving blood."  Phone : +33 (0)1 49 70 99 72 – Mobile : +33 (0)6 52 84 44 70 Email : sebastien.han@xxxxxxxxxxxx – Skype : han.sbastien Address : 10, rue de la Victoire – 75009 Paris Web : www.enovance.com – Twitter : @enovance
On Jun 11, 2013, at 7:43 PM, Oliver Francke <Oliver.Francke@xxxxxxxx> wrote: Hi, _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com |
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