I have Home assistant installed on a SD card (with Home Assistant OS) and the data stored on a connected SSD disk. I need a reinstall of my SD card because HA crashed daily.
How can I rebuild such a configuration?
You can navigate to Settings → System → Backups
and create a full backup of your configuration, addons and integrations. You have to take the backup file from the sd card before formatting it, with a program like WinSCP
Otherwise, you can install and configure the Home Assistant Google Drive Backup addon so you will be able to download backups from your Google Drive (the easiest way)
So, after reinstalling home assistant, restore the backup you have. Instructions here: How to restore a backup - Community Guides - Home Assistant Community (home-assistant.io)
I was mainly concerned that data disk is already separated from SD card.
But now I have rebuild a new SD card and start Raspberry from newly build SD card. The data disk will be automatically found and all is in place. 
The only thing I had to do is correct my IP configuration. Really cool
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Hi,
i have the same situation. Got a new Odroid n2+ replacing a broken one.
Also use a fresh SD Card with new flashesd 11.4
Attached everything back including the SSD Datadisk and fired it up.
Its just starting with onboard. Here I can create a new instance or restore a backup.
It seems that the disk was not automaticly detected.
What i’m doing wrong?
Edit: The disk is listed under ha os datadisk list
On the SSD itself there is one ext4 partition with name hassos-data-dis
What have i to do that hass will just use that disk? Is there some config file on the SD Card?
BR
This worked for me.
When you replace the old OS disk with new OS install then after boot HAOS will give a warning that there are 2 data disk (one in the new OS disk and another the original data disk) attached to device.
Home Assistant can automatically repair it if ‘Submit’ is pressed in the warning.
It basically would rename the data disk from new OS disk that is not supposed to be used.