How did you work that out?

Using Victoria, a quick sequential scan of my 1TB SSD at an average speed of 219 MB/s took 51 seconds.

I'm guessing that the OP's run lasted about 400 - 450 seconds, which would mean that the dips are 90 seconds apart. My feeling is that some task is touching the drive at 90 second intervals. The drive's APM setting would be less than this.

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A backup a day keeps DR away.

hm, never used victoria, as well as 'quick sequential scan', so this might be a problem. I assumed it is a full scan of all the data area, my mistake.. :s
If it is 90 seconds, it is most probably due to smart attribute autosave.
This can be disabled with Smart cmd 0xD2.

Attr autosave should have different sound than head unload, so it would be nice to listen to head movements, first without disk access (unload should take place in 90 seconds if our suspect is right), then with surface scanning for example (only SA access should be heard, slight head sound).

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Adatmentés - Data recovery

Do the BIOS test first. That will tell us if the drive is touching itself (!) every 90 seconds, or if an OS task or software application is touching it.

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A backup a day keeps DR away.

well, i have bios test done. Nothing, attr isnt change at all. In fact after i reboot into OS and even read 100tb from this drive the attr is the same. It stopped growing right after i disconnect it (logically) from my chia farm.

It might have something to do with idle_b settings but i can't find any tool to manage this with Toshiba drives.

Your drive is a rebadged HGST model (as is your 8TB WD drive). Look for Hugo or Niagara tools.

ftp://atxlab.ddns.net/ftp/hdd/hgst/

Your BIOS test seems to prove that SMART autosave is not responsible for the load/unload cycle count. Instead it appears to be caused by some OS task or application software.

BTW, your SMART report suggests that your drive is rated for 1 million load/unload cycles and 40,000 power-on hours.

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A backup a day keeps DR away.

what does it mean exactly rebadged? is it bad thing?

link isn t working also it looks scary as hell, ftp really?

During the HGST buyout by WD, HGST was making 3.5" drives for Toshiba. WD now puts its own brand on HGST drives. Look at the part number on the PCB and search for it.

As for FTP, use FileZilla, or you can set up FTP access in Windows' File Explorer.

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A backup a day keeps DR away.