A Synology volume showing a Crashed status does not automatically mean all data is gone - it means the storage pool can no longer guarantee data integrity in its current state and needs action before it is safe to use. The word Crashed is DSM's (Synology's operating system) way of saying a volume has reached a state it cannot recover from automatically. What you do in the next few minutes determines whether the data is recoverable. Stop writing to the NAS and read this guide before attempting any repair.
In short: A Crashed volume does not always mean permanent data loss. Degrade is survivable - replace the failed drive and rebuild. Crashed from file system errors (all drives healthy) is often fixable with DSM's built-in repair. Crashed from multiple drive failures may need professional recovery. The first rule: stop writing to the volume immediately and identify the cause before taking any action.
Stop writing to the volume immediately. Every write operation to a crashed or degraded volume risks overwriting data that could otherwise be recovered. Power down the NAS if you are not sure what action to take next. A powered-off NAS with a crashed volume is safer than an active NAS where data might be written to a partially failed array. Do not attempt to repair, rebuild, or reinitialise the volume until you understand the cause of the failure.
Understanding Synology Volume Status Levels
DSM uses different status labels to indicate how serious a volume problem is. Each has a distinct meaning and requires different action. Treating a Degraded volume like a Crashed volume (being overly cautious) wastes time. Treating a Crashed volume like a Degraded volume (being insufficiently cautious) risks permanent data loss.
| Normal | Volume is healthy. No action needed. |
|---|---|
| Degraded | One drive has failed in a RAID 5 or RAID 6 group. Volume is still readable and writable. Replace the failed drive to rebuild. |
| Critical | RAID 5 with a second drive failure, or RAID 6 with a third failure. Volume may be readable but at risk. Act immediately - another failure means data loss. |
| Crashed | Volume can no longer guarantee data integrity. May be caused by multiple drive failures beyond RAID tolerance, file system corruption, or SHR/storage pool integrity failure. |
| Read-only | DSM has detected a file system error and automatically dropped the volume to read-only to prevent further corruption. Data may be recoverable. |
| Unmounted | Volume cannot be mounted. Often appears after an unexpected power loss or when DSM cannot complete the file system check on boot. |
Step 1: Identify the Cause Before Taking Action
Open Storage Manager in DSM and check the health status of each individual drive, not just the volume. Go to Storage Manager, then HDD/SSD, and look at the condition of every drive. A Crashed volume with all drives showing Normal suggests file system corruption rather than a drive failure - different problem, different fix. A Crashed volume with one or more drives showing Failed or Warning indicates drive failure as the likely cause.
Check the Synology system log. Go to Log Center in DSM and look at the System or Storage logs for error messages around the time the volume status changed. Log entries like Drive 1 failed or Volume 1 degraded provide a timeline of what happened. This log is essential for communicating the situation to Synology support or a data recovery service if you need outside help.
Step 2: The Degraded Volume Path
A Degraded volume has lost one drive in a RAID 5, SHR, or RAID 1 array. The volume is still readable and writable - your data is intact. The urgency is real (a second failure while degraded destroys data) but you have time to buy the correct replacement drive and wait for it to arrive.
Identify which drive failed (it will show a red or orange indicator in Storage Manager). Remove it and replace it with a drive of equal or greater capacity. For SHR volumes, the replacement must be at least as large as the failed drive. Do not replace with a smaller drive. Once the new drive is inserted, DSM will detect it and offer to rebuild the storage pool - accept and let the rebuild complete.
Rebuilding a degraded RAID 5 volume takes 6-24 hours per terabyte of array size. During the rebuild, the volume remains accessible but performs more slowly. Do not power off the NAS during a rebuild. If a second drive fails during the rebuild, the array is lost - back up your data to an external drive before the rebuild if you have an external drive available.
Step 3: The Crashed Volume Path
A Crashed volume has exceeded RAID tolerance - typically two drives failed in a RAID 5 array, or three drives failed in a RAID 6 array, or a single drive failed in a RAID 0 or RAID 1 with no remaining redundancy. The data on the volume may be partially or fully unrecoverable without professional tools.
Do not reinitialise the volume. DSM may offer a Repair or Reinitialise option for a Crashed volume. Reinitialising wipes all data and creates a fresh empty volume - this is a permanent, unrecoverable action. Only reinitialise if you have verified your backup copy is complete and you are starting fresh intentionally.
If you do not have a current backup and need the data, contact a professional data recovery service before doing anything further. Services like Payam Data Recovery, Platinum Data Recovery, or international specialists like DriveSavers have tools to recover data from failed NAS arrays that DSM cannot access. Powering the NAS back on after a Crashed state and attempting self-repair can reduce your chances of successful recovery by overwriting sectors that would otherwise be readable.
File System Errors vs Drive Failures
If all drives show Normal health but the volume is Crashed or mounted as read-only, the problem is a file system error rather than a drive failure. RAID (a method of spreading data across multiple drives so the system survives a drive failure) protects you from drive hardware failures - it does not protect against file system corruption, which can happen after an unexpected power loss, a software bug, or a failed DSM update.
Synology's built-in repair tool is the first line of defence for file system errors. In Storage Manager, select the volume and look for a Check File System or Repair option. Running this on a read-only mounted volume is lower risk than running it on an actively crashed volume. DSM's fsck (file system check) can repair many types of corruption without data loss.
If you lost power during a write operation (power cut, NAS was unplugged, UPS failed), this is the most common cause of file system corruption on an otherwise healthy RAID set. DSM runs an integrity check on boot - let it complete without interruption. If DSM's repair completes successfully, the volume returns to Normal status. If DSM's repair fails, the file system damage is beyond what the built-in tool can fix.
Using Synology's Diagnostic Tools
Synology provides several diagnostic tools accessible from DSM that help determine whether recovery is possible without external help. The S.M.A.R.T. test in Storage Manager gives a per-drive health assessment. Run a short test first (2-5 minutes) and look at the attributes section - Reallocated Sector Count, Uncorrectable Sector Count, and Pending Sectors above zero are warning signs of drive degradation even if the drive has not yet fully failed.
The Scrub function in Storage Manager runs a data integrity check on the storage pool, comparing parity data to stored blocks and repairing any inconsistencies it finds. Running a scrub on a Normal or Degraded volume is a maintenance practice that catches and corrects minor inconsistencies before they cause problems. On a Crashed volume, scrub cannot run - the volume is already past the point where scrub is applicable.
When to Call Professional Data Recovery
Professional data recovery is worth considering when: the volume is Crashed due to multiple simultaneous drive failures, DSM's built-in repair fails or makes the situation worse, the data has no recent backup and is critical, or the drives themselves show physical failure symptoms (clicking, grinding, or not spinning up).
Professional data recovery for a multi-drive NAS array ranges from a few hundred dollars for logical recovery to several thousand dollars for physical media damage requiring cleanroom work. Reputable Australian services include Payam Data Recovery and Platinum Data Recovery. Before calling, document the drive failure timeline from DSM's log, note the RAID type and number of drives, and do not attempt any further repair actions - each failed attempt reduces the chance of successful recovery.
How to Prevent This in Future
A UPS (uninterruptible power supply) connected to your NAS is the single best prevention for file system corruption. Power outages and spikes are the leading cause of unexpected NAS shutdowns that trigger file system errors. A UPS gives the NAS 5-20 minutes of battery time to complete active writes and shut down cleanly when mains power fails.
Regular S.M.A.R.T. testing and storage scrubs catch early drive degradation before it causes a volume crash. Synology's DSM can be configured to run S.M.A.R.T. tests on a schedule - weekly tests catch drive health changes before they become critical. Enable the Send notifications when storage health changes option so you receive an email when a drive enters warning status, not after it has already failed.
Finally, a current backup to a separate location is the ultimate protection. A RAID array protects you from a drive failure. It does not protect you from simultaneous drive failures, ransomware, accidental deletion, or physical destruction of the NAS. The 3-2-1 backup rule - three copies, two media types, one offsite - remains the right framework even when you have RAID redundancy locally.
Related reading: our NAS buyer's guide and our Synology brand guide.
Related reading: our NAS explainer.
Can I recover data from a Crashed Synology volume myself?
It depends on the cause. If the crash was due to file system corruption with physically healthy drives, Synology's built-in fsck repair often recovers the volume without data loss. If the crash was due to multiple drive failures beyond RAID tolerance, self-recovery tools have low success rates and can worsen the situation. For critical data on a multi-drive failure scenario, professional data recovery services have the best success rates because they image each drive before attempting any reconstruction.
My Synology shows one drive failed and the volume is degraded. Is my data safe?
Yes, for now. A single-drive failure in a RAID 5, SHR, or RAID 1 volume leaves the data intact and accessible. The urgency is that a second drive failure while degraded will take the volume to Crashed status. Replace the failed drive as soon as possible and let the array rebuild. Buy a known-good NAS-rated drive (IronWolf or WD Red Plus) and insert it while the NAS is running - hot-swap is supported on Synology. The rebuild will start automatically once the new drive is detected.
How long does rebuilding a degraded Synology RAID take?
Rebuild speed depends on drive capacity and NAS processor speed. A rough estimate is 6-15 hours per terabyte of storage pool size. A 4x4TB RAID 5 array (12TB raw, 8TB usable) rebuilding after a single drive failure can take 48-72 hours to complete. The NAS remains accessible during the rebuild with reduced performance. Do not power off the NAS during the rebuild process.
DSM is offering to Repair my Crashed volume. Should I do it?
It depends on what caused the crash. If multiple drives failed, clicking Repair typically initiates a reinitialisation that will erase all data. If the crash was due to file system errors with healthy drives, the Repair function runs an fsck check and may recover the volume. Before clicking Repair, confirm the cause of the crash in the Storage Manager logs and verify whether drives are physically failed or just showing a software status issue. If you are unsure, do not click Repair on a Crashed volume without a current backup in hand.
Will Synology support help recover data from a crashed volume?
Synology's support team can assist with diagnosing the cause of a crash and providing guidance on DSM's repair tools, but they cannot recover data from physically failed drives - that requires physical media examination that only specialist recovery labs can perform. Synology support is online-only in Australia (no phone support). Submit a ticket via the Synology support portal with screenshots of Storage Manager and the system log, and they will typically respond within 1-2 business days.
Is RAID 6 significantly better protection than RAID 5 for a 4-bay NAS?
Yes, for a NAS that stores important data. RAID 6 uses two drives for parity rather than one, which means it can survive two simultaneous drive failures without data loss. RAID 5 can only survive one. With modern hard drives, the probability of a second drive failure during the rebuild of the first is not negligible - the rebuild process stresses all remaining drives heavily. For a NAS storing data you cannot afford to lose, RAID 6 or SHR-2 is the more defensible choice on a 4-bay or larger NAS. The cost is one additional drive's worth of usable capacity.
Australian Buyers: What You Need to Know
Professional data recovery services in Australia include Payam Data Recovery and Platinum Data Recovery, both with experience in NAS array recovery. International services including DriveSavers and Ontrack can also handle Synology arrays if no suitable local service is available. Data recovery costs vary widely by fault type - logical recovery (file system errors, healthy drives) is typically $300-800. Physical media recovery (drive head failure, platter damage) requiring cleanroom work ranges from $1,500-5,000 depending on the number of drives and severity.
Replacement drives for a Synology NAS are available from Mwave, Scorptec, and PLE. Seagate IronWolf and WD Red Plus are the standard recommendations for consumer and SMB Synology NAS builds. Australian Consumer Law applies to drive purchases, covering you for warranty and manufacturing defect claims beyond the manufacturer's standard warranty period. When replacing a failed drive, keep the failed drive until the rebuild is complete and verified - do not discard it until you have confirmed the rebuilt array is healthy.
Want to understand RAID protection levels and which to choose for your NAS? The RAID explained guide covers RAID 1, 5, 6, and SHR with recommendations for each use case.
NAS RAID Explained