Re: [Xen-users] [XCP] XCP 1.5 Beta Create Local SR

["Nick Couchman" <Nick.Couchman@xxxxxxxxx>]

>   xe sr-create content-type=user device-config:device=/dev/sda3 
> host-uuid=47f5967d-76c9-4e66-b6e6-543afcf1c19e name-label="Local storage" 
> shared=false type=lvm
> 
> I have a concern that that's fragile; add or subtract a USB
> stick or another disk or whatever and what is /dev/sda
> *might* change.  The device is used to create a pbd; here's
> the relevant output from my machine:

Oh, yes, depending on how XCP picks up the disks when you reboot the
system, this could be very fragile.  Theoretically, if you're using LVM
(NOT Thin Provisioning), it should *scan* the disk devices and find the
LVM one located wherever that disk happened to get attached.  However,
this would mis-match what the XE Toolstack thinks the disk should be, so
how does the system recover from that??

> 
> xe pbd-list">pbd-list ->
> 
> uuid ( RO)                  : a844364c-fc70-f4ce-4ca1-785224cf7dc4
>              host-uuid ( RO): 75de5d76-0011-4296-85b1-100567147c46
>                sr-uuid ( RO): e77ffc8a-ed78-c9b0-7ed4-702308cce130
>          device-config (MRO): device: 
> /dev/disk/by-id/scsi-3600508e0000000006069ef5986d41402-part3
>     currently-attached ( RO): true
> 
> [...]
> 
> uuid ( RO)                  : da707dd6-d1cf-a460-cc76-6ca55f413813
>              host-uuid ( RO): 75de5d76-0011-4296-85b1-100567147c46
>                sr-uuid ( RO): 2415abc5-7d90-10e5-49db-39cc21c4eba0
>          device-config (MRO): device: /dev/disk/by-id/scsi-35000c50033e2ff7f
>     currently-attached ( RO): true
> 
> In the first one, the 3rd partition is used and I gather XCP
> 1.5 has the same layout with Dom0 in partition 1, partition
> 2 is of identical length (used for a backup command?) and
> the third, comprising the rest of the disk, was left for
> the Local storage sr.  Perhaps someone who's installed 1.5
> could provide us with a listing from the relevant pdb so
> that we can see how it's done in this version?
> 
> In the second I just gave it the whole disk.  In reflection, I'm
> not sure that was a good idea (vs. a partition using the
> whole disk), it violates the normal usage; can't remember
> why I did it.
> 
>   This should have been done at install time by the
>   installer, so not sure if this is a bug or just a glitch
>   during the install I was doing?
> 
> I would think the former; that's how 1.1 works (and as I
> recall it didn't give you an option *not* to create a local
> repository, although strictly speaking in a proper XCP cloud
> your VMs' storage is going to be separate so that you can
> easily migrate them and so forth).  You might want to try a
> raw installation again to see if if you've found a bug or if
> 1.5 just allows an option not to create a local sr.

You actually can uncheck the box to create the SR on the local disk, but
I'm pretty sure I did not do this.  I did install XCP on a few nodes to
SDHC cards, and I did not want any local repository being created, so I
was able to untick the box and go through the install without the local
repo.  

-Nick



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