Table of Contents

SnapRAID - Scrub for Bit Rot

Over time, files can become corrupted due to bit rot.

Scrub

sudo snapraid scrub

NOTE: This command verifies the data in your array comparing it with the hash computed in the “sync” command.

  • Every run of the command checks about the 8% of the array, but not data already scrubbed in the previous 10 days.

Scrub using different options

The -p, –plan option can be used to specify a different amount, and the -o, –older-than option to specify a different age in days.

For example, to check 5% of the array older than 20 days use: 

sudo snapraid scrub -p 10

NOTE: Scrubbing should be run periodically to catch issues before they become serious.

  • -p 10: limits scrubbing to 10% of files, reducing disk wear.

Errors found during a scrub

If during the scrub process, silent or input/output errors are found, the corresponding blocks are marked as bad in the “content” file, and listed in the “status” command. 

snapraid status

To fix them, you can use the “fix” command filtering for bad blocks with the -e, –filter-error options: 

snapraid -e fix

NOTE: At the next “scrub” the errors will disappear from the “status” report if really fixed.

  • To make it fast, you can use -p bad to scrub only blocks marked as bad: 
    snapraid -p bad scrub

WARNING: Take care that running “scrub” on a not synced array may result in errors caused by removed or modified files.

  • These errors are reported in the “scrub” result, but related blocks are not marked as bad.