Synology cache failure
Synology SSD cache can be read-only or read-write depending on configuration and DSM generation. A failed read cache is mainly an availability issue, while a failed write cache can involve acknowledged data not yet committed to the backing pool.
Understand the symptom
Read-only cache can be repopulated from the pool, but read-write cache may hold dirty blocks and uses redundancy to protect them. After power loss or member failure, cache metadata and the backing filesystem may represent different transaction points.
What you may see
One or more cache members are absent, failing, or not assembling.
DSM restricts writes because cache or storage state cannot be trusted.
Recent writes may not be fully represented on the backing pool.
DSM recognizes dependencies or an incomplete cache state.
Protect the source
Write-cache data may not yet exist on the storage pool.
New setup can erase evidence needed to map prior cache state.
Databases and VMs can issue new writes as soon as the volume returns.
Do this now
Pause VMs, containers, databases, sync, backups, and shared-folder access.
Save cache mode, RAID type, dirty state, pool status, SMART data, and event logs.
Record serials, bays, removal history, and which SSD failed first.
Keep chassis, boot media, cache SSDs, pool disks, and power components together.
NEPFOSYS process
NEPFOSYS identifies read-only versus write-back behavior and member chronology.
Cache and backing members are preserved before detach, repair, or pool assembly.
Candidate views are tested against Btrfs or ext4, databases, VMs, and priority files.
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
Normally it mirrors data from the pool, but the pool and exact DSM state still require evaluation.
Not until cache mode, dirty state, member health, and preservation options are understood.
Preserve all originals first; a rebuild or recreation changes cache state.
DFW local · Nationwide mail-in