<div dir="ltr"><div>Oops. I missed the note when I went through the core. Sorry everyone for the incorrect information I provided earlier about libgfapi.</div><div>And thank you Niels for bringing up the correct information.</div><div><br></div><div>Regarding libvirt parsing the provided XML; according to a table provided under [1], a source of type `gluster` can have only one host.</div><div>So it seems, libvirt doesn't support backup volfile servers. I haven't been able to find any information on qemu's support, so I'm assuming it doesn't support backup volfile servers either.</div><div><br></div><div>~kaushal</div><div><br></div><div>[1]: <a href="https://libvirt.org/formatdomain.html#elementsDisks">https://libvirt.org/formatdomain.html#elementsDisks</a></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jan 28, 2015 at 3:11 PM, Niels de Vos <span dir="ltr"><<a href="mailto:ndevos@redhat.com" target="_blank">ndevos@redhat.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">On Wed, Jan 28, 2015 at 02:06:32PM +0530, Pranith Kumar Karampuri wrote:<br>
> Added Niels and Shyam who may know about this.<br>
><br>
> Pranith<br>
> On 01/27/2015 12:25 PM, Arash Shams wrote:<br>
> ><br>
> >is there anyone pay attention to my question ?<br>
</span>> >------------------------------------------------------------------------<br>
<span class="">> >From: <a href="mailto:ara4sh@hotmail.com">ara4sh@hotmail.com</a><br>
> >To: <a href="mailto:gluster-users@gluster.org">gluster-users@gluster.org</a><br>
> >Date: Sun, 25 Jan 2015 08:16:49 +0000<br>
> >Subject: [Gluster-users] how to Set BackupVol for Libgfapi ??<br>
> ><br>
> >Hello<br>
> >is this possible ??<br>
> > <disk type='network' device='disk'><br>
> > <driver name='qemu' type='qcow2' cache='none'/><br>
> > <source protocol='gluster' name='vol1/vms/disks/cmsrm-ui01.qcow2'><br>
> > <host name='141.108.36.19' port='24007'/><br>
> > <host name='141.108.36.20' port='24007'/><br>
> > <host name='141.108.36.21' port='24007'/><br>
> > <host name='141.108.36.22' port='24007'/><br>
> > </source><br>
> > <target dev='vda' bus='virtio'/><br>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x05'<br>
> >function='0x0'/><br>
> > </disk><br>
> >so when one server goes down my vm dont goes down !!!<br>
<br>
</span>This is intepreted by libvirt, and I do not know if the syntax is valid<br>
or how libvirt does this.<br>
<br>
libgfapi offers this functionality by calling glfs_set_volfile_server()<br>
a number of times with different servernames/addresses:<br>
<br>
<a href="https://github.com/gluster/glusterfs/blob/master/api/src/glfs.h#L134" target="_blank">https://github.com/gluster/glusterfs/blob/master/api/src/glfs.h#L134</a><br>
<br>
Note that the specified server is only a single-point-of-failure when<br>
the initial connection to the volume is made. Most users seem to use<br>
round-robin-DNS or a virtual IP-address (with some HA/failover solution)<br>
to prevent this SPOF.<br>
<br>
After connecting, the client knows about all the servers that are part<br>
of the volume. If one server goes down, others will be used<br>
automatically.<br>
<br>
If one brick of a replica goes down, there will be a timeout (by default<br>
42 seconds) until an other brick is tried. Depending on the<br>
configuration of the storage inside the VM, you could run into read-only<br>
filesystems whan such a failover happens.<br>
<br>
>From the Gluster side, you could try tuning the network.ping-timeout<br>
option. Or inside the VM you can set a SCSI-timeout per disk (in a sysfs<br>
file like /sys/block/sda/device/timeout), you'll need a udev-rule or<br>
something to make the change premanent.<br>
<br>
HTH,<br>
Niels<br>
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