Direct-SATA BU40N + Dune Part Two UHD live testing exposed that the
v0.17.3 single-shot SCSI READ path matched 0/22 of the small bad-
sector LBAs that dd if=/dev/sr0 recovers on the same drive. This
release closes that gap and fixes adjacent bugs silently capping
recovery.
- /dev/sr0 pread fallback in Drive::read (Linux only): on SCSI READ
Err, fall back to posix_fadvise(DONTNEED) + pread() against the
corresponding block device. Kernel sr_mod runs ~5 internal retries
with no per-attempt mid-layer escalation overhead — the mechanism
behind dd's recovery advantage. End-to-end byte verification
confirms the fallback path returns real disc data.
- Disc::patch per-range watchdog fix: MAX_RANGE_SECS was breaking
'outer (one slow range killed the entire patch). Now skips to the
next range. Pre-fix patch died after 4 sectors of range 1 of 47.
- Per-sector range budget: range_budget = sectors × 25 s, capped at
1800 s. Replaces the flat 180 s/range that was unfair to medium
ranges and pointlessly generous to single-sector ones.
- consecutive_failures resets per range. The wedge-exit detector is
for stuck-on-one-range, not many-small-ranges-with-one-fail-each.
- Reverted inline 5× retry experiment (was hurting: each retry paid
kernel SCSI escalation overhead). Restored READ_RECOVERY_TIMEOUT_MS
to 60 s. The kernel-auto-retry pattern is now provided by sr0
fallback.
Empirical: pass 1 recovered 94.6 MB / 11 s of main title (33 sr0
saves). Pass 2 added 0.6 MB. Remaining ~233 MB on the test disc
appears physically unrecoverable on this hardware.
MattJackson
a35596d2d1