storage
- Prune a stale synced copy with an rsync checksum dry run
A push-direction rsync --dry-run -c gives each top-level entry of an old copy a verdict; delete only what the source holds identically, git index aside.
- Measure real btrfs disk use without sudo
Get the real on-disk size of a btrfs path, after compression and reflinked copies, by running the host's compsize in a rootful Docker container.
- 12.4 GB of duplicates, 3.4 GB on disk
On compressed btrfs, du and a duplicate finder overstated what deleting would free, and a permission error hid 15.8 GB. compsize, without sudo, told the truth.
- Salvaging a dying disk by partitioning around the wound
A drive SMART calls dead had all 58 bad blocks in the first 5% of the platter. Read the map, partition past the wound, reclaim 6.7 TiB.
- Reallocated sectors: is your drive dying or just scarred?
One drive had 344 reallocated sectors, the other had zero. The one with zero was dying. The raw count lies; the delta under a forced write pass tells the truth.
- Stop chasing a sensor that doesn't exist
The LSI SAS2008 HBA cooking itself has no temperature sensor. No tool, driver, or root binary conjures a number that was never wired to the die.
- All four drives at once, and why that was the good news
Every HDD on the storage box vanished at once — a quadruple drive death, it looked like. It was two mundane faults stacked together, and the data was fine.