I have got reason to be proud of me.
I did!
Firstly, I installed spare ssd disk and add one as new SR (ext3).
[for those looking for an adventure up their own arse]
this morning was started disgustingly
all VMs have forgot their disks (CPU presents, RAM and LAN too, DISK absent (0 kb)) and did not started.
I honestly tried to use my "copy(es) of images" - IMG-files I wrote about above (do not ask me how these IMG-files was created - I don't know).
It did not works directly. System did not recognize IMG-files as something useful.
I converted my IMG-files to vhd
qemu-img convert 53ab0887-3dba-47e9-a3c0-7d04f9fe71b0.img -O vpc -o subformat=dynamic 53ab0887-3dba-47e9-a3c0-7d04f9fe71b0.vhd
Ok, last week one of my VM had 20 Gb of disk space (now no disk at all). I added new empty 20 Gb disk to VM. And then "Import VDI" just converted vhd-file to newborn 20 Gb disk.
Voilà! VM started!!!
[/for those looking for an adventure up their own arse]
After all my VM started NORMALLY (!) (backup works and creates gigabytes' sized backup, snapshots work too) I migrated all VM to new SR.
There are some questions I would like to clarify:
New SR - SR I created today, right SR;
Old SR - bad SR (/ls), where IMG-files are.
1. Although I have migrated all my VM to new SR, IMG-files are still at old SR. I would like to remove old SR and create a new (right, ext3) one instead.
So, when I remove these IMG-files if I don't get into another round of trouble (something like "i won't start. where is my starting image?")?
2. One of my acquaintances insists on that SR should be under RAID. At least "mirror". I have OS's volume with "mirror" and about 2 Tb of unused space there.
So, is RAID necessary for SR?
And, is it a good idea to place SR at system disk (RAID1)?
And how can I set a selected SR as default?
Upd1
@olivierlambert said in [Solved] Yet another question about Backup - why so small backup created with XOA?:
How did you create the SR?
In the status of this SR was one interesting string "legacy=yes". I suppose this explains how I reached this unusual result (IMG-files which nobody beside me did not see before, very small backup etc)
Upd2
I have answered to my questions by myself
(firstly, migrate everything to a new SR, set it as default if necessary
xe pool-param-set uuid=xxxx default-SR=xxxx
)