6 ms·

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

by geokon 11mo ago

fainpul 11mo ago
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 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 11mo ago
  /dev/null is "empty" if you read it, its /dev/zero you dont want to dd onto your disk.
homebrewer 11mo ago
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 11mo ago
  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).
deleted 11mo ago
[deleted]
easygenes 11mo ago
This is the most straightforward reliable option: > sudo dd if=/dev/sdX of=/dev/null bs=4M status=progress iflag=direct
- tensility 11mo ago
  This.

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

by geokon 11mo ago

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

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 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 11mo ago
/dev/null is "empty" if you read it, its /dev/zero you dont want to dd onto your disk.

homebrewer 11mo ago

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 11mo ago
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).

deleted 11mo ago

[deleted]

easygenes 11mo ago

This is the most straightforward reliable option: > sudo dd if=/dev/sdX of=/dev/null bs=4M status=progress iflag=direct

tensility 11mo ago
This.