Recovery and volumes

Recovery and volumes

Reed–Solomon recovery record (-rr)

PArc writes Reed–Solomon parity (parc-rs1). It repairs contiguous damage and scattered sectors, not just one sector per group.

parc a backup.parc data -rr3%       # ~3% of the size as parity
parc a backup.parc data -rr10       # 10 sectors of 512 bytes
parc a backup.parc data -rr10m      # 10 MB of parity
parc a backup.parc data -rr10;4096  # 10 sectors of 4096 bytes
parc a backup.parc data -rr-        # no recovery record
parc a backup.parc data -rr0%       # CRCs only: detect, do not repair

Without -rr, the default depends on size (4%, 2% or 1%). parc r archive.parc verifies and writes fixed.<name> if there is damage; the original is never touched. It returns 2 when damage exceeds what the record can repair.

Volumes (-v)

parc a backup.parc data -v100m
parc x backup.parc.001 -dp/out

• It is the same archive split into .001, .002…; cat backup.parc.0* > backup.parc (or copy /b on Windows) rebuilds it.
• Updating a volume set keeps the volume size and deletes extra volumes.
• -rr protects the whole set; parc r writes a single-file fixed.<name>.
• -v cannot be combined with stdout (-) or SFX creation (which no longer exists).

See Options and Encryption.