On Wed, Jan 28, 2015 at 02:06:32PM +0530, Pranith Kumar Karampuri wrote: > Added Niels and Shyam who may know about this. > > Pranith > On 01/27/2015 12:25 PM, Arash Shams wrote: > > > >is there anyone pay attention to my question ? > >------------------------------------------------------------------------ > >From: ara4sh@xxxxxxxxxxx > >To: gluster-users@xxxxxxxxxxx > >Date: Sun, 25 Jan 2015 08:16:49 +0000 > >Subject: how to Set BackupVol for Libgfapi ?? > > > >Hello > >is this possible ?? > > <disk type='network' device='disk'> > > <driver name='qemu' type='qcow2' cache='none'/> > > <source protocol='gluster' name='vol1/vms/disks/cmsrm-ui01.qcow2'> > > <host name='141.108.36.19' port='24007'/> > > <host name='141.108.36.20' port='24007'/> > > <host name='141.108.36.21' port='24007'/> > > <host name='141.108.36.22' port='24007'/> > > </source> > > <target dev='vda' bus='virtio'/> > > <address type='pci' domain='0x0000' bus='0x00' slot='0x05' > >function='0x0'/> > > </disk> > >so when one server goes down my vm dont goes down !!! This is intepreted by libvirt, and I do not know if the syntax is valid or how libvirt does this. libgfapi offers this functionality by calling glfs_set_volfile_server() a number of times with different servernames/addresses: https://github.com/gluster/glusterfs/blob/master/api/src/glfs.h#L134 Note that the specified server is only a single-point-of-failure when the initial connection to the volume is made. Most users seem to use round-robin-DNS or a virtual IP-address (with some HA/failover solution) to prevent this SPOF. After connecting, the client knows about all the servers that are part of the volume. If one server goes down, others will be used automatically. If one brick of a replica goes down, there will be a timeout (by default 42 seconds) until an other brick is tried. Depending on the configuration of the storage inside the VM, you could run into read-only filesystems whan such a failover happens. From the Gluster side, you could try tuning the network.ping-timeout option. Or inside the VM you can set a SCSI-timeout per disk (in a sysfs file like /sys/block/sda/device/timeout), you'll need a udev-rule or something to make the change premanent. HTH, Niels
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