f you don't run the filesystem checker, the apparent corruption in the filesystem may get worse. Unchecked, this can lead to data corruption or at the unlikely worst destruction of the filesystem. During the filesystem check, file structures within the filesystem will be checked, and if necessary repaired. The repair takes no account of content; it's all about making sure the filesystem is self-consistent. If you run e2fsck -y /dev/sdc you have no opportunity to validate the corrections being applied. On the other hand if you run e2fsck -n /dev/sdc you can see what would happen without it actually being applied, and if you run e2fsck /dev/sdc you will be asked each time a significant correction needs to be applied. In summary
If you ignore the warning and do nothing, over time you may lose your data If you run with -y you have no option to review the potentially destructive changes, and you may lose your data If you run with -n you will not fix any errors, and over time may lose your data, but you will get to review the set of changes that would be made If you run with no special flag you will be prompted to fix relevant errors, and you can decide for each whether you are going to need direct professional assistance Recommendation
Run e2fsck -n /dev/sdc to review the errors Decide whether this merits a subsequent e2fsck /dev/sdc (or possibly e2fsck -y /dev/sdc ) or whether you would prefer to obtain direct professional assistance
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