Synology Btrfs metadata capacity
Btrfs separates data and metadata allocation. Snapshots, small files, churn, and copy-on-write updates can consume metadata space differently from ordinary capacity, leaving DSM unable to complete transactions or mount the volume normally.
Understand the symptom
Btrfs tracks extents, checksums, directories, roots, and snapshots in metadata trees. A filesystem can have apparent data space while lacking usable metadata allocation or while a tree block is unreadable. Recovery evaluates RAID health, chunk allocation, transaction generations, and snapshot roots before attempting mutation.
What you may see
Overall storage remains, but metadata allocation or tree consistency prevents writes.
Operations cannot reserve or update required metadata.
Transaction, tree-block, or allocation failures appear in logs.
Mount protection or failed transaction replay blocks normal access.
Protect the source
Chunk relocation adds heavy reads and writes to a filesystem already short on metadata.
Cleanup can fail while changing the very trees needed for recovery.
Databases and indexes may generate rapid copy-on-write updates.
Do this now
Pause snapshots, backup, sync, indexing, packages, containers, VMs, and client writes.
Save pool and volume status, allocation details, logs, snapshots, disk health, and recent changes.
Record bay order and keep every current, removed, spare, and replacement disk.
Do not balance, check with repair, recreate, or delete snapshots before protected copies exist.
NEPFOSYS process
NEPFOSYS reviews member health, RAID state, Btrfs chunks, roots, and transaction generations.
Storage members are preserved before metadata-changing operations.
Reachable trees, snapshots, and priority shares are reconstructed from the most consistent state.
A clear next step
Start a case with the exact symptoms, incident timeline, prior attempts, encryption details, and the files that matter most. NEPFOSYS will route the case to the appropriate DFW intake or nationwide mail-in path.
Start with a case reviewQuestions, answered
Btrfs allocates data and metadata in separate chunks; one class can become constrained before total capacity is exhausted.
It also requires metadata transactions and can worsen an unstable state. Protect the source first.
Balance is a filesystem maintenance operation, not a preservation step, and it rewrites substantial allocation data.
DFW local · Nationwide mail-in