Re: [Qemu-devel] [PATCH 1/1] block/gluster: add support for multiple gluster backup volfile servers

[Deepak C Shetty <deepakcs@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 3275 bytes --]



On 09/08/2015 08:40 PM, Deepak Shetty wrote:
>
>
> On Tue, Sep 8, 2015 at 8:32 PM, Daniel P. Berrange 
> <berrange@redhat.com <mailto:berrange@redhat.com>>wrote:
>
>     On Tue, Sep 08, 2015 at 06:34:09PM +0530, Prasanna Kumar Kalever
>     wrote:
>     > This patch adds a way to specify multiple backup volfile servers
>     to the gluster
>     > block backend of QEMU with both tcp and rdma transport types.
>     >
>     > Problem:
>     >
>     > Currenly VM Image on gluster volume is specified like this:
>     >
>     > file=gluster[+tcp]://server1:24007/testvol/a.img
>     >
>     > Assuming we have have three servers in trustred pool with
>     replica 3 volume
>     > in action and unfortunately server1 (mentioned in the command
>     above) went down
>     > for some reason, since the volume is replica 3 we now have other
>     2 servers
>     > active from which we can boot the VM.
>     >
>     > But currently there is no mechanism to pass the other 2 gluster
>     server
>     > addresses to qemu.
>     >
>     > Solution:
>     >
>     > New way of specifying VM Image on gluster volume with backup
>     volfile servers:
>     >
>     > file=gluster[+transport-type]://server1:24007/testvol/a.img\
>     > ?backup-volfile-servers=server2&backup-volfile-servers=server3
>
>     Comparison with RBD syntax:
>
>       file=rbd:pool/image:auth_supported=none:\
>         mon_host=mon1.example.org
>     <http://mon1.example.org>\:6321\;mon2.example.org
>     <http://mon2.example.org>\:6322\;\
>     mon3.example.org <http://mon3.example.org>\:6322,if=virtio,format=raw
>
>     As Peter already mentioned, you're missing port numbers.
>
>     It is slightly unpleasant to have different ways of specifying the
>     first
>     vs second, third, etc hosts. I wonder if it would be nicer to keep all
>     the hostnames in the host part of the URI. eg
>
>      file=gluster[+transport-type]://server1:24007,server2:3553,server3:2423/testvol/a.img\
>     ?backup-volfile-servers=server2&backup-volfile-servers=server3
>
>     Of course it ceases to be a wellformed URI at that point, so
>     another option
>     would be to just allow the host part of the URI to be optional,
>     and then
>     accept mutliple instances ofa  'server' arg, eg
>
>      file=gluster[+transport-type]:///testvol/a.img\
>     ?server=server1:2424&server=server2:2423&sever=server3:34222
>
>
> Is it allowed to have this syntax and be a valid URI ? I admit i 
> haven't looked at the
> URI rfc for a long time now, hence the Q. Also looking at rbd syntax, 
> it looks
> to follow this model already is it ? Whats the difference between 
> using ':' to
> separate key=value pairs Vs using '?" query syntax ? Should we look at 
> having
> a uniform way of specifying URI be it rbd or gluster or sheepdog ... ? 
> If yes
> what that uniform syntax be using ':" or '?" ?

Answering myself, based on what I figured .... :)
Looks like rbd syntax is a propertiary one and not adhering to URI rfc, 
while gluster syntax
is URI compliant so the 2nd option suggested by danpb seems good

Also need to ensure that old syntax of providing server:port in the 
authority field should
be honoured so that older clients/apps generating the old syntax won't 
be broken

thanx,
deepak


[-- Attachment #2: Type: text/html, Size: 7150 bytes --]