@olivierlambert thanks.
When I typed "I leave how suggestion for improvement.", I wanted say "suggestion for nexts releases".
I 'm not a programmer, I'm sorry. I can only say my experiences of use.
My English is very poor. I don't want to sound offensive. I'm sorry.
Hello everyone.
The last week, i needed restore a one vdi from delta backups. This VM has a three vdis.
I restored a full VM for recovered a particular vdi.
I don't know if possible restore one vdi from VM's delta backup from XOA's restore GUI or command line.
If don't possible, I leave how suggestion for improvement.
regards.
@olivierlambert Also, I thing others ways.
Make a script in XCP host what run ping to VMS'S ip and force reboot of VM when ping is not respond.
What do you think about this?
hello @olivierlambert
( What do you mean exactly for a VM that doesn't respond?)
For example, when the SO of guest is freeze. (for different reasons ej: driver error, low quality software, etc).
(Xen will detect if a VM is crashing already, and will reboot it.)
where can I read information for this?
Hello everybody!!!
I want automatically reboot VMs when they are broken (no respond).
I don't know if xcg-ng has process or script for that cases.
I saw something in the web with ssh but maybe xcp-ng has something else.
You can help me?
Perhaps nfs has to options for restart connection when that is disconnect.
But I don't find option for this.
Thanks @olivierlambert , in south America the internet and energy services sometimes fails. 
Hello, can you help me? please
I need setting XOA for remote nfs backups.
My situation is what nfs target is not all time online. In general all fridays is down.
On saturday the target is online, but when the backups need write in nfs target return error, for example:
Error: Unknown system error -116: Unknown system error -116, mkdir '/run/xo-server/mounts/11934fec-f3a1-4f7f-a78d-00eeb1b39654'
I tested more options, but none is ok.
The last XOA’s remote settings tested is: vers=4.2,soft,rw,retry=3,async,proto=tcp,noexec,nosuid,soft,bg,timeo=30
and the server’s /etc/exports is:
media/bkpf/backup 172.16.112.2(rw,all_squash,anonuid=2000,anongid=200)
Right now, I need go to XOA's remote setting and change option manualy (From Enable, to Disable and later Enable) of target for remount target and later the backup can write ok on target.
In the image you can see the bkpm target state on saturday.
How to setting XOA for remount nfs target automatlly before the backup run?
The XOA's version are xo-server 5.80.0 and xo-web 5.84.0
thank's for your attention.
@fachex said in VDI_IO_ERROR(Device I/O errors) when you run scheduled backup:
@olivierlambert no more feedback on this problem. We reinstall the whole server, XCP-ng 8.2 and we are still experiencing this problem. We are unable to do Delta backups.
Hi @fachex, @stormi
If you update XCP-ng, remember that the installation cleared all settings in XCP-NG (Host).
In my case, XCP-NG deleted the folders where the mount point of the external device was.
Maybe this information will help you in your LVM permission problem.
@olivierlambert said in suggestions for future upgrade...:
web hooks
Thank @olivierlambert
I'm going to read about web hooks in xoa. 
Hi,in this days i'm work hard with VMs backups from xoa interface.
I think about is a good idea be able to add bach scripts in XOA backup screen so these run before and after each backup run.
I hope to be clear. 
Hi good day.
I have an installation of XCP-ng 8.1, xo-server 5.57.3 and xo-web 5.57.1
When I want to make delta backups of VMs of more than 500GB it gives me the following error:
VDI_IO_ERROR (Device I / O errors)
Look for the solution on the internet without success.
I ran several tests and found that I had the Timeout = 1 option set to advanced options.
This caused the backup to be canceled in one hour. But the information in the backup status was as follows:
transfer
Start: May 3, 2020, 4:15:46 PM
End: May 3, 2020, 5:15:11 PM
Duration: an hour
Error: VDI_IO_ERROR (Device I / O errors)
The error makes no mention of timeout cancellation. What disorients the search for the problem.
The solution, put extend the value in timeout or set it to zero and the backup worked correctly.
(Sorry for the translation, it is done with google translation) 