Asustor + Btrfs + R/W cache = data loss risk

[migueldc]

So, this is the 2nd time in 2 years that I have lost some important data on my Asustor AS6510T

I have 5x 18Tb drives in Raid 5 , Btrfs and 2x 1Tb SSD for caching

First time was in 2022 with during the Deadbolt attack, but the data loss was not due to Deadbolt (although a few less important files), but due to the ADM update to fix it :
- after the attack, the NAS hung for 30mins in the initialization phase, so I couldn't install the ADM update
- removing the SSDs made it start up with the new ADM but did not recognize my Volume 1 (corrupted)
- after trial and error, I put the SSDs back in and it suddenly recognized my Volume 1 again although some files were lost

Last week, I bought 2x extra 18Tb to increase my volume size and upgrade to Raid 6
- I did "safely remove cache" in ADM, but after 30mins, it was still suck on 0%
- So I had no other resort than trying a hard reboot (in hindsight I should have waited for hours, but who would expect a 1Tb SSD flush would take hours..) and that's when my Volume 1 was inaccessible
- I took the SSDs out, rebooted and back in and then it recognized my Volume 1
- I then safely remove my SSDs (this time it took 15mins)
- ADM started immediately a rebuild
- after the rebuild, I got a weird status (see attached pics) :

• RAID Level RAID 5 : Drive 1, 2, 3, 4, 5, 5 (2 times 5!!)
  
• RAID 5, data protection None (Faulty drives tolerated 0), even though I have 5x disks of 16.37 Tb (18Tb) and a total volume capacity of 65.47 Tb.
  

After the 4 day Quin Ming holidays, Asustor support will investigate my volume, see if any date is lost
In the meantime I bought 4 extra disks to copy all my data to.

Asustor clearly stated : Btrfs in combination with R/W cache can corrupt your disk if the SSDs are removed (or fail)
Now, that I would call a HUGE security risk and as a product manager myself I cannot understand why ADM does not warn the users at all or even better, would restrict the use of R/W cache in combination with Btrfs


After copying my data over, I will probably delete the current volume (crashed 2 times, don't trust it anymore) and create a clean
new volume

So my questions to the forum are :
- Should I use Ext4 instead instead of Btrfs ? Is it really safer ? Strangely enough, the same Asustor support told me Btrfs is fine and is actually a good fs. Really after what they said ??
- I will probably not use Cache (or at least not R/W cache) ever again...
- or should I just get rid of my Asustor and go back to Synology or build a NAS myself with TrueNAS ?

Any tips here ? people with same experiences ?

What would be the safest NAS (Synology, TrueNAS) and safest Filesystem ?
Plz, take into account mirroring is not an option with +60Tb data, but Raid 6 is

[ed]

It's disheartening to hear about your data loss experiences with your Asustor NAS setup. Indeed, combining Btrfs with R/W cache on Asustor systems can pose a significant risk, as you've unfortunately experienced firsthand. While Asustor support may have touted Btrfs as a robust file system, the reality of potential data corruption when using R/W cache demands caution. Considering your situation, migrating to Ext4 could offer a safer alternative, as it doesn't involve the same risks associated with Btrfs and cache usage. Additionally, refraining from employing cache, especially R/W cache, seems prudent to mitigate any further data loss risks. As for your NAS choice, both Synology and TrueNAS offer compelling options. Synology's DS1821+ or DS3622xs+ could be worth considering for their robust hardware and reliable performance, while TrueNAS provides a more DIY approach if you're inclined to build your NAS solution. Ultimately, prioritizing data integrity and reliability should guide your decision-making process.