[Gluster-users] how to Set BackupVol for Libgfapi ??

[Kaushal M]

Oops. I missed the note when I went through the core. Sorry everyone for
the incorrect information I provided earlier about libgfapi.
And thank you Niels for bringing up the correct information.

Regarding libvirt parsing the provided XML; according to a table provided
under [1], a source of type `gluster` can have only one host.
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.

~kaushal

[1]: https://libvirt.org/formatdomain.html#elementsDisks

On Wed, Jan 28, 2015 at 3:11 PM, Niels de Vos <ndevos at redhat.com> wrote:

> 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 at hotmail.com
> > >To: gluster-users at gluster.org
> > >Date: Sun, 25 Jan 2015 08:16:49 +0000
> > >Subject: [Gluster-users] 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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