[easygenes]

So say I have a 4TB USB SSD from a few years ago, that's been sitting unpowered in a drawer most of that time. How long would it need to be powered on (ballpark) for the full disk refresh to complete? Assume fully idle.

(As a note: I do have a 4TB USB SSD which did sit in a drawer without being touched for a couple of years. The data was all fine when I plugged it back in. Of course, this was a new drive with very low write cycles and stored climate controlled. Older worn out drive would probably have been an issue.) Just wondering how long I should keep it plugged in if I ever have a situation like that so I can "reset the fade clock" per se.

[gblargg]

More certain to just do a full read of the drive to force error correction and updating of any weakening data.

[geokon]

noob question... how do i force a full read?

[homebrewer]

the most basic solution that will work for every filesystem and every type of block device without even mounting anything, but won't actually check much except device-level checksums:

  sudo pv -X /dev/sda

or even just:

  sudo cat /dev/sda >/dev/null

and it's pretty inefficient if the device doesn't actually have much data, because it also reads (and discards) empty space.

for copy-on-write filesystems that store checksums along with the data, you can request proper integrity checks and also get the nicely formatted report about how well that went.

for btrfs:

  sudo btrfs scrub start -B /

or zfs:

  sudo zpool scrub -a -w

for classic (non-copy-on-write) filesystems that mostly consist of empty space I sometimes do this:

  sudo tar -cf - / | cat >/dev/null

the `cat` and redirection to /dev/null is necessary because GNU tar contains an optimization that doesn't actually read anything when it detects /dev/null as the target.

[medoc]

Just as a note, and I checked that it's not the case with the GNU coreutils: on some systems, cp (and maybe cat) would mmap() the source file. When the output is the devnull driver, no read occurs because of course its write function does nothing... So, using a pipe (or dd) maybe a good idea in all cases (I did not check the current BSDs).

[easygenes]

This is the most straightforward reliable option:

> sudo dd if=/dev/sdX of=/dev/null bs=4M status=progress iflag=direct

[tensility]

This.

[fainpul]

On macOS / Linux you can use `dd` to "copy" everything from /dev/yourssd to /dev/null. Just be careful not to do it the other way!

https://www.man7.org/linux/man-pages/man1/dd.1.html

I have no idea if forcing a read is good / the right way. I'm just answering how to do it.

[justincormack]

/dev/null is "empty" if you read it, its /dev/zero you dont want to dd onto your disk.