NAS froze during check up synchronizing F4-210

[orochikun]

Got my NAS to finally accept RAID5 but the while synchronizing volume around 30% there was a long beep and I restarted the NAS.

Questions

Can I force a syncronization ?
Can that be affecting speed ?

4 HGST 10TB drives current transfer speed is 20-30 MB/s

[TMSupport]

Does the array continue to sync when you reboot the device? Is RAID5 newly created or migrated? Please check that your hard drive is plugged in tightly.
Please refer to the article to troubleshoot the issue about transfer speed.

[orochikun]

Does the array continue to sync when you reboot the device? No , status just stays all good
Is RAID5 newly created or migrated? Newly created
All HDD are properly seated, the pool has not displayed any error
The link does not help for the speed . unfortunately ... can I remove the HDDs and install new ones to see if the issue are the HDD ( and not loose anything ?)

[TMSupport]

A status of "Good" means that the synchronization has been completed. Can you see that the array mode is RAID 5 in the volume or storage pool information?

[orochikun]

The only problem with good is that it did not complete 100% if alarmed long beep and I had had to shutdown the device from the power wall
Yes I can see the RAID 5 mode is set

[orochikun]

Just rebooted the NAS and now 2 HDD are missing :S
With RAID error

https://imgur.com/a/V5X56C0

*Also I just noticed that I posted in the wrong section sorry *

[TMSupport]

Please check whether HDD3 and HDD4 are recognized normally. You can check whether the indicator light of the hard disk is on. Go to Control Panel > Storage Manager > Hard Drive to check whether the hard disk is in good condition.
If the hard disk is not recognized, please shut down the device, unplug and insert the hard disk, and restart.
If both HDD3 and HDD4 fail, the array cannot be recovered.