https://bugs.kde.org/show_bug.cgi?id=520897
Bug ID: 520897
Summary: BD-R/BD-R XL: filesystem defaults and multisession
interaction unsuitable for modern archival workflows
Classification: Applications
Product: k3b
Version First 26.04.1
Reported In:
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: Data Project
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Target Milestone: ---
**Version:** K3b 26.04.1
**Platform:** Linux (Fedora Silverblue, x64; tested with Pioneer BDR-XD08U,
Verbatim BD-R XL TL 100 GB)
---
**Summary**
K3b's filesystem defaults and multisession workflow are still aligned with
CD/DVD-era assumptions. When burning BD-R / BD-R XL with realistic archival
workloads (tens of thousands of files, some with long names), several issues
compound to produce silent burn failures, unreadable appends, and require users
to abandon the GUI for command-line tools (`growisofs`) to recover. This report
covers three related problems and suggests fixes.
---
**Problem 1: Rock Ridge filename collisions silently break large burns**
With the default filesystem (ISO 9660 + Rock Ridge + Joliet),
`mkisofs`/`genisoimage` truncates filenames to fit Rock Ridge limits (~103
characters). When multiple files in a directory share a long common prefix
(common with automated capture filenames, scientific data, scraped content),
they collapse to identical names post-truncation and `mkisofs` aborts.
User-visible behaviour:
- K3b displays the error "Could not determine size of resulting image file." —
Elapsed time 00:00:53, 0% progress.
- Root cause appears only in the debug output: multiple "Error: ... and ...
have the same Rock Ridge name" lines.
- The UI gives the user no actionable information.
This affects any sufficiently large archive of files with structured naming.
---
**Problem 2: No UDF default for BD-R / BD-R XL**
K3b applies CD/DVD-era filesystem defaults regardless of the detected media.
UDF has been the native filesystem for Blu-ray since the BD specification and
is the de facto standard for archival use, but K3b:
- Does not default to UDF when the inserted media is BD-R or BD-R XL.
- Does not suggest UDF.
- Does not warn that the default ISO 9660 + Rock Ridge filesystem is
inappropriate for the medium.
Users have to know to manually enable UDF in Project Properties → Filesystem
tab.
---
**Problem 3: Multisession requires ISO 9660 but doesn't tell the user**
K3b's "import previous session" feature requires reading the ISO 9660 directory
structure of the existing disc. If the previous burn used pure UDF (e.g., as a
workaround for Problem 1), the multisession import fails with:
> "Medium is not multi session and does not contain ISO 9660, cannot emulate
> multi session"
https://www.reddit.com/r/linux4noobs/comments/k12936/k3b_cannot_burn_more_files_onto_a_bluray_disc/
This is misleading — the medium *is* multisession-capable (`dvd+rw-mediainfo`
reports `appendable`). The actual issue is K3b's GUI workflow being unable to
read pure UDF for its import step. Users then fall back to `growisofs -M -udf`
from the command line, which produces an appended session that is not mountable
by default by the Linux UDF driver (mount requires `-o session=N`), effectively
wasting the disc.
This combination of issues is silently set up at the *first* burn (when
filesystem is chosen) but doesn't manifest until the *next* burn (when
multisession import fails). The user has no opportunity to learn the constraint
at the relevant time. Sadly I wasted an expensive and scarce 100GB Bluray MDISC
on this.
---
**Reproduction**
1. Create a Data Project in K3b 25.x with BD-R XL inserted.
2. Add a folder containing several thousand files where some long filenames
share a common prefix of 100+ characters.
3. Burn with default filesystem settings (ISO 9660 + Rock Ridge + Joliet).
4. Burn fails with "Could not determine size of resulting image file."
5. As workaround, change filesystem to UDF only and re-burn. Burn succeeds.
6. Later, attempt a multisession burn against the resulting disc.
7. K3b refuses with "cannot emulate multisession."
8. Fall back to `growisofs -M /dev/sr0 -udf ...`. Burn completes.
9. Mount the disc: only the first session's contents are visible. The appended
session is on the disc but requires `mount -o session=2` to read.
---
**Suggested fixes**
1. **Auto-default to UDF + ISO 9660 + Joliet (with Rock Ridge disabled) when
target media is BD-R or BD-R XL.** This combination supports long filenames via
Joliet, is fully multisession-capable via K3b's existing workflow, and matches
what commercial archival pipelines use. Rock Ridge has no useful role on
Blu-ray for the vast majority of users.
2. **Cross-validate filesystem choice with multisession setting at project
time.** If a user selects "Start Multisession" but the filesystem doesn't
include ISO 9660, surface a warning *before* the first burn — not after the
second burn fails. Either auto-correct or require explicit confirmation.
3. **Improve error surfacing for `mkisofs` filename collisions.** When
`mkisofs` aborts due to Rock Ridge name collisions, parse the debug output and
present a meaningful error in the UI ("X files have names that conflict under
Rock Ridge truncation; either rename them or disable Rock Ridge"). Currently
the user has to manually open Show Debugging Output and read the raw stderr.
4. **Detect BD media on project creation and offer a one-time recommendation**
to use BD-appropriate defaults.
Items 1 and 2 alone would prevent this entire class of failure.
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