Read a tape

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Read a tape

This page takes one cartridge from the drive to a tar file of its backup. It uses captures/mytape as the working name; use any name, but keep the files under captures/ (Keep captures private).

Output marked (example output) shows the format the command prints with plausible values, not a real session.

Prerequisites

  • The tools installed, with the tw and qicsilver aliases (Install the tools).
  • The Greaseweazle flashed and the drive wired and powered (Flash the Greaseweazle, Wire up a drive).
  • A clean head and capstan. Old tapes shed oxide, and every pass over a failing tape costs something. Clean before a valuable tape goes in; see A dirty head.
  • Free disk space. A capture is roughly 50 MB per track of a short QIC-80 cartridge, and more for longer and faster tapes.

Step 1: Check the board

Run tw info.

tw info

The firmware line should show a protocol version and a capability list. If it says stock Greaseweazle (no Tapewyrm verbs), flash the Tapewyrm firmware first. With more than one Greaseweazle plugged in, pass --port PORT before the subcommand.

Step 2: Load the cartridge

Insert the cartridge and wait for the drive to finish its own load sequence. The drive winds the tape to find its reference holes; this can take 30 seconds or more.

Step 3: Wake the drive

Run tw drive select.

tw drive select

[12:00:00] INFO     auto: trying default: no wake steps
           INFO     auto: default: no answer (command 6: no ACK bit -- ...)
           INFO     auto: trying colorado: phantom select 0, enter primary mode
           INFO     auto: drive answered colorado; using profile 'colorado'
status : 0x25 [ready cartridge_present referenced]
select : yes -- cue INDEX every 2.9 ms

(Example output.) auto logs each wake-up it tries and the one the drive answered. The rest of this page names the profile with --profile colorado; use the one your drive answered, or the one its drive page names. To stop typing it, set it in the config file.

Step 4: Read the drive's reports

Run tw drive status.

tw --profile colorado drive status

cleared on wake: 26 Power On Reset Occurred (process error)
drive status : 0x25 [ready cartridge_present referenced]
last error   : 0x001a -> 26 Power On Reset Occurred (process error)
drive config : 0x90 -> 500 kbps, QIC-80 bit set
rom version  : 0x5c -> version 92
vendor id    : not supported by this drive (no ACK)
tape status  : not supported by this drive (no ACK)

(Example output.) Check three things:

  • ready and referenced in drive status. referenced means the drive has found the tape's reference holes. tw dump refuses to start without it. If it is missing, run tw --profile colorado drive load-point, which can take 30 seconds or more.
  • The rate in drive config. tw dump records at the rate the drive reports. QIC-40 and QIC-80 tapes are 500 kbps, QIC-3010 is 1 Mbps and QIC-3020 is 2 Mbps.
  • tape status, if the drive answers it. tw dump with no track list takes the track count from the tape format reported here.

Older drives do not answer every report. not supported by this drive (no ACK) is normal for those. Each field is described in tw drive.

Note

The Colorado 1400 on the bench refuses the QIC-80 rate and format (error 31) and has not read a QIC-80 tape. Dump QIC-80 tapes on a QIC-80 drive such as the Jumbo 350. See Colorado 1400.

Step 5: Look at track 0 first

The header and the volume table are at the start of track 0, so one track is enough to see what the tape holds and whether it reads at all.

tw --profile colorado --progress dump --check captures/mytape 0

--check also decodes the pass and stops if fewer than 80% of its sectors are CRC-clean. Expect a few minutes for a short QIC-80 cartridge: the pass winds to the track's start, then runs the tape end to end.

Step 6: Dump the whole tape

Dump every track into the same directory. --no-clobber skips track 0, which is already there.

tw --profile colorado --progress dump --retries 2 --no-clobber captures/mytape

[12:00:01] INFO     drive: config 0x90 -> 500 kbps, tape QIC80; writing TWRF to captures/mytape
           INFO     no tracks named: dumping all 28 tracks of this QIC80 tape
           INFO     track  1: winding to its start...
[12:00:40] INFO     track  1: wound to its start in 38.9s
           INFO     track  1: capturing -> captures/mytape/track-01.twrf
[12:03:09] INFO     track  1: 47.6 MB in 149s; checking...
[12:03:14] INFO     track  1: END EOT, 147.3s of tape, 207 segments by INDEX, 0 missed in gaps
           ...
done: 27 tracks, 5589 segments by INDEX -> captures/mytape

(Example output.)

  • With no track list, tw dump dumps every track of the format the drive reports: QIC-40 20, QIC-80 28, QIC-3010 and QIC-3020 40. If the drive does not report the format, the dump refuses to start; name the tracks, for example 0-27.
  • Each track is one pass, written to captures/mytape/track-NN.twrf. captures/mytape/dump.jsonl gets one line per pass.
  • --retries 2 reads a track up to two more times when its pass fails a health check, and keeps the best pass.
  • After every pass tw checks, without decoding, that the pass ended at the end of the tape and found about as many segments as the best pass so far. If not, it stops rather than wear a failing tape further.
  • A whole QIC-80 tape takes an hour or more. A track of a 1,000 ft QIC-3020 cartridge takes about 9 minutes, plus winding.

If the dump stops with dump stopped: track N: ..., read the reason, clean the head, and run the same command again: --no-clobber skips the tracks already dumped clean and reads again the one it stopped on.

On a tape you expect to be damaged, keep every read instead of only the best: --passes 2 --retries 2. All the options are in tw dump.

Step 7: Make a tape image

Convert the captures to a TWTZ image. This step needs no hardware.

tw --progress convert -j 0 captures/mytape captures/mytape.twtz

Sources come first and the image last, as with cp. tw convert decodes every capture, places each sector by its own address, applies the Reed-Solomon error correction, and writes the image. -j 0 decodes as many captures at once as the cores and the RAM allow. Expect about a quarter of the tape's running time with one job.

The last lines of the log summarise the result:

INFO     header: segment 0 (clean), tape name (none), format code 4
INFO     geometry: 40 tracks x 1475 segs/track = 59,000 segments
INFO     segments: 1,445 clean, 12 corrected, 14 uncorrectable, 57,431 missing, 98 bad (map)

missing counts segments on tracks that were not dumped. uncorrectable segments had more bad sectors than the error correction can repair. Dump those tracks again into a new directory and convert both directories together:

tw --profile colorado dump captures/mytape-pass2 5,9
tw convert captures/mytape captures/mytape-pass2 captures/mytape.twtz

A sector read on any pass fills the gaps of the others. See tw convert.

Step 8: Identify the tape

qicsilver identify captures/mytape.twtz

identify prints the tape name, the cartridge type, the format and last-written dates, the bad-sector map, and the volume table: one row per backup volume, with its number, date, size, compression and description. Note the volume numbers. If the volume table reads as nonsense, see Wrong volume profile. Every field is described in qicsilver identify.

Step 9: Extract the volumes

qicsilver --progress extract captures/mytape.twtz captures/mytape-vols

extract writes one captures/mytape-vols/vol-NN.twvl per volume, where NN is the volume's number in identify. Bytes from segments that were not recovered become recorded holes, so nothing after a hole shifts. See qicsilver extract.

List a volume before you write a tar:

qicsilver inspect captures/mytape-vols/vol-00.twvl

See qicsilver inspect.

Step 10: Write the tar

qicsilver --progress tar captures/mytape-vols/vol-00.twvl captures/mytape.tar

captures/mytape.tar: 2000 files, 150 directories, 12 damaged (report: captures/mytape.tar.damaged.txt)

(Example output.) The tar keeps the backup's paths, modification times and DOS attributes. The damage report beside it lists every file that lost bytes (lost) or that the original backup software could not read (error). A lost file can come back if you dump its tracks again and merge; an error file cannot. See qicsilver tar.

tar and inspect also take the image directly, without extract: qicsilver tar captures/mytape.twtz captures/mytape.tar --volume 0.

Step 11: Release the drive

Phantom drives stay selected after tw exits. Release the drive before you switch to another one on the same cable:

tw drive deselect

Next steps