SSD data retention long term

[Donnie Fisher]

Whilst I'm far from being a data hoarder, there is data I would like to keep longer term and primarily its photos and similar that currently sit on an ssd mirror pair zfs pool in unraid. The SSD's are fairly new, and I intend to keep them long term, and trim is enabled. The SSD's replaced 2Tb hard drives I'd had for more than 10 years.

On the assumption that the unraid machine will generally remain powered, is there anything that I ought to do to manage the data on the ssd drives longer term? SSD drives lose their data slowly if left unpowered going by what the web says. But do they lose data if a file isn't used for long periods ? or does an SSD automatically go around and check things like that.

To be clear, I'm not talking about backups, archives methods etc. Its just that if I dont read a file for a long time on an SSD ... is there a risk to the data being lost long term even though the drive remains powered ?

 

[Tetras]

But do they lose data if a file isn't used for long periods ? or does an SSD automatically go around and check things like that.

To be clear, I'm not talking about backups, archives methods etc. Its just that if I dont read a file for a long time on an SSD ... is there a risk to the data being lost long term even though the drive remains powered ?

I think you'd have to look at the datasheets / technical manuals for controllers to find out what they do in the background, since I doubt they're all the same.

From what I can gather, when you read from the cells it will know if there's degradation.

If you never read from those cells, you'd be reliant on whatever else it does.

You could try asking here:

https://www.reddit.com/r/NewMaxx/comments/dhvrdm/ssd_guides_resources/

I know they've actually read some of these documents

 

[Donnie Fisher]

From what I can gather, when you read from the cells it will know if there's degradation.

If you never read from those cells, you'd be reliant on whatever else it does.

Thats exactly what I'm wondering ... and whether I should be doing some sort of read-scan across all files on a periodic basis.

[Edit]

Went down the rabbit hole. Its not clear on whether SSD controllers will automatically scan and refresh stale data sat on a drive. It does seem to be the case though that when data is read, the controller will consider whether its degraded, and if so, will refresh it. Similarly, if a data block is read multiple times without being re-written to, then each read is assumed to degrade the data, and after a set number of reads, it will refresh it anyway as well.

I then read that btrfs has a command to scan across all data blocks, which would prompt a read of all data ... and so could trigger checks for degradation ... and then it also mentioned ZFS had a similar with the scrub command. Scrub reads all data, and compares it against that data's checksum, correcting anything it finds. Unraid has scrub options and for my system its enabled and set for monthly.

So as it stands, it seems for my setup that monthly scrub will read all data and as a result:
- That read command will make the controller check for degradation and correct.
- ZFS will check and correct against checksums.
- Multiple scrubs over files which aren't being used in a long time may eventually trigger a re-write by default too.

So I'm a little happier about it now that long term retention has mechanisms in place to ensure bit-rot is hopefully addressed.

 

[leezer3]

If you want an IMHO, I wouldn't trust a SSD for long term retention of anything important.
ZFS scrubs are OK in principle, but if the drive has lost the data it's not coming back no matter what.
Parity data only works if that's not gone too, which with a pair of mirror disks, if you've lost one, then you've most likely lost both.

BTRFS I wouldn't touch with someone else's bargepole (they're changing the on-disk format *again*)

 

[Donnie Fisher]

I totally get your point, which is why there are other options as backup.

But in terms of a day to day use, the nas would typically be my 1st place to go for looking back through stuff on the rare occasions and to have a little assurance that it should be there is good enough for me the moment.