Hi!

Please, help me to understand the following (my question is after
the quotation; I am new to all this, and will be grateful for the help):

Slack space sanitizers sanitize disk blocks (and portions of
disk blocks) that are not part of any file and do not contain
valid file system meta-information. For example, if a 512-
byte block holds a file’s last 100 bytes and nothing else, a
slack-space sanitizer reads the block, leaves bytes 1–100 untouched,
and zeros bytes 101–512.
I am not sure I understand the numbers:
if a 512- byte block holds a file’s last 100 bytes
does it mean that there was some file of some size, and only
its last 100 bytes still exist (say, the file had 300 bytes, so the only
ones seen now are from 200 byte to 300 byte, i.e. last 100 bytes),

and these 100 bytes now occupy 1 - 100 of 512 byte block?

If so, why sanitizer doesn't zero these 1-100 bytes; aren't these
considered as important ones that hold the information?

Thank you!