We already wrote about Volume Crashed and Repair, about a dead NVMe write-back cache, about a controller Rebuild, and about RAID 5 with two drives down. This is the earlier screen. The pool is still up. Redundancy is already gone. The update looks like the responsible click.
Degraded means the files are still being served
Synology's repair article defines it. A storage pool becomes Degraded when one or more of its drives becomes defective, and the pool remains accessible because no data loss has occurred. Repair is how they say you return that pool to a healthy status, and the defective drive is replaced before you start. The Repair option appears only when the pool is Degraded.
Crashed is the next status. The same article says that once a storage pool is Crashed, you can no longer repair it yourself. The volume-crash article, updated September 29, 2026, is blunter about the volume: a crash caused by drive errors or file-system errors cannot be repaired. Shares that still open are the degraded case. Shares that do not are the crashed-volume page. The update is how people spend the first one and arrive at the second.
How many drives that takes depends on the pool you built. Synology's RAID-type table says a two-drive RAID 1 tolerates one failure, RAID 5 (three or more drives) tolerates one, and RAID 6 (four or more) tolerates two. SHR-1 with two or more drives tolerates one. SHR-2 needs at least four drives and tolerates two; the repair article says an SHR-2 array can withstand two drive failures. Their word on the banner is still "one or more," so read the drive list instead of assuming it means a single disk. A pool that has used up that tolerance is already Degraded with nothing left to lose. The Degraded status is the window. An update spends it on a reboot.
Synology's pre-update check is a Healthy drive
The article "What should I do before updating my Synology storage system," updated September 17, 2026, puts drive health in the mandatory list. Drives should be in a Healthy status. The place they name is Storage Manager > HDD/SSD. The same list says to read the release notes, and that once you have updated you cannot roll back to a previous version. The recommended half says to back up first, because an improper shutdown during the update can lose data, and to avoid I/O-heavy work during the update. The examples they give include repairing or expanding a volume.
A Degraded pool fails that check. The defective drive is why the status exists. Installing DSM to clear the banner ignores the line Synology printed above the download.
Their System Update help splits what the screen is offering. A major update includes new features, performance enhancements, critical bug fixes, and security patches: Download, then Update Now. A minor update is security and bug fixes, and a message appears next to Status. Updates that fix critical security issues are labeled an important version, and Update Settings can install those by themselves. The help page also says you can only update to a newer version, and that updates are irreversible. It says updating the system does not affect the data on the NAS, and in the same paragraph it says to create a backup before you start. Both sentences are theirs. The backup has to exist before the restart. A degraded pool is the case where you do not yet have it.
"Automatically install the latest updates" stays on the current DSM version. The note on that option says it will not, by itself, move the NAS to a new major version. It can still install an update that restarts the box. On Synology devices released in 2024 and earlier, the setting that does not install is "Notify me and let me decide whether to install the new update." On devices released in 2025 and later, the important-update notification includes a postpone link. Each link works once. The install can be postponed for up to 28 days from the first notification. The system checks daily and installs at the scheduled time. Leaving a degraded NAS powered on through that window is how the update happens with nobody at the keyboard.
The manual path restarts too. The tutorial updated December 26, 2025 says Control Panel > Update & Restore > Update, then the manual update button, and the system restarts automatically when the update is complete. The DSM 7 help labels that control Manual DSM Update. Current DSM release notes say the same thing in the important notes: 7.4.1-90080 Update 1 says "This update will restart the device." Version 7.4.1-90080 (July 23, 2026) and 7.4-90075 (June 16, 2026) each say the update will restart the Synology NAS, and that after installing it you will not be able to downgrade. Some older notes say the restart depends on the model. We will not pretend every build Synology has ever shipped reboots every chassis. The update in front of a current box, and the manual update you install yourself, is documented as a restart.
The install writes the system partition on the member disks
DSM does not live on a hidden USB stick inside a typical NAS. Synology's article "Which drive is the DSM operating system installed on" says every drive you install contains the system partition: the DSM operating system, user settings (account credentials, network settings, Control Panel settings), and system logs. The partition article, updated September 29, 2026, says that on most models the system uses RAID 1 mirroring and saves an identical copy onto every drive. If drives are damaged, startup uses the system data from a healthy drive. If more than one drive is healthy, the smaller drive number is used first. Their example is Drive 1 ahead of Drive 4.
That "every drive" sentence has the exceptions they print under it. Drives in an expansion unit contain the system partition and store no system data. The HD6500, SA3400D, and SA3200D store the operating system and system settings only on dedicated system drives or SATA DOMs. The RC18015xs+ stores them on drives in an RXD1215sas. Models running DSM use up to 12 drives to assemble the system. DSM Enterprise (PAS) can use all installed drives. Creating an SSD cache, or adding a drive to one, creates a data partition and not a system partition. A Plus-series or DS desktop unit with a handful of SATA disks in SHR is the common case of the rule: the system partition is a mirror across those disks.
The data partition is the other slice. The pool and the volume are there, and that article says your data and installed packages are stored there too. The update is a different write. Their insufficient-capacity article says the error you get when an update cannot unpack is a lack of room to unzip and install update files in the system partition. The free space Storage Manager shows for the volume is not that space. The article covers three installs in one sentence: the system OS, packages, and the firmware of Synology drives.
A pool drive is a system-partition member until DSM takes it out. The HDD/SSD help says Action > Deactivate Drive removes the drive from the storage pool, the volume, and the system partition. It also says the drives of a pool cannot be deactivated once the pool has reached its maximum fault tolerance, because deactivating another drive crashes the pool. A RAID 1, RAID 5, or single-redundancy SHR that is already Degraded is on that line for every drive still in the pool. If the failed drive's status is not yet System Partition Failed, that drive can still be in the system mirror. The update installs into the mirror members that are still in it.
System-partition health is a separate banner from pool health, and the two show up on the same afternoon. The system-partition article, updated September 18, 2026, says System partition degraded means the partition on some drives is inaccessible and at least one drive is still healthy. RAID 1 is why that degrades instead of crashing. Overview says "The system partition has degraded. Click the link to repair it." On HDD/SSD, from DSM 7.2 on, the drive status becomes System Partition Failed. The HDD/SSD help tells you to click Repair System Partition. A note on the system-partition article says Overview hides that Repair link when something more urgent already needs to be handled. Read the words on the screen. Repairing the system partition rebuilds that mirror. Do not start it, and do not start a DSM update, as a way to tidy a disk the pool has already called defective.
Storage Manager and Hybrid Share are the same install
Storage Manager 1.0.0-0017, published September 26, 2023, moved Storage Manager into a package. The same note says that if a firmware update is required for Synology drives, it is performed automatically during the DSM update, and the NAS has to be on the internet for that to happen. We will not stretch a 2023 package note into a claim about every DSM build shipped since. What the current HDD/SSD help still says is enough: if the firmware status is Update required, Action > Firmware Update, then Update. If those Synology drives are in use — assigned to a storage pool, or hot spares — a system restart is required. That restart is the same class of event as the DSM reboot, aimed at disks that are already short one member.
The drive database is a smaller button on the same page, under HDD/SSD > Settings > Advanced, Update Now. The help says updating that database does not affect drive performance. It is a compatibility list. It does not replace a defective drive, and it does not make a Degraded pool Healthy. Leave Firmware Update alone. Leave the DSM update alone. A clicking drive gets powered off before either screen is worth a click. See what a clicking drive means.
Hybrid Share is a package. Hybrid Share 1.5.0-1817, published July 15, 2025, fixed an issue where Hybrid Share might fill the system partition and stop other packages from working. That sentence is a fix for a bug in older package builds. It is not a warning that today's Hybrid Share is filling the partition. The part that still applies is the insufficient-capacity article: a package update installs its files in the system partition. We did not find a current Synology document that says the Hybrid Share or Storage Manager screen silently starts a DSM upgrade. If what you are looking at is an Update button for DSM, for Storage Manager, for Hybrid Share, or for drive firmware, the pool status is the thing to read first. Degraded means the button waits.
A restart is how a degraded pool becomes a crashed one
Synology's update help says a completed update leaves the data in place. Their pre-update article names the failure they want the backup for: an improper shutdown during the update. Their volume-crash article, updated the same month, lists how a volume actually crashes. On the drive side: a defective drive removed from the pool once the number of removed drives has reached the RAID's fault tolerance; too many drives pulled by hand; an SSD read-write cache that crashed or was unmounted improperly; incompatible drives. On the file-system side: errors after an unexpected power loss or from drives that already had read-write errors, memory problems, or a Btrfs volume moved to a model that does not support Btrfs.
A degraded pool is already partway down that list. The remaining disks are the whole array. The update restarts them, and it writes the system partition on the ones still in the mirror, including a disk Storage Manager has already called defective. We are not going to invent a DSM version that rewrites md, LVM, or Btrfs on disk. We did not find a release note that says an update does that to a degraded hard-drive pool. What we did find is narrower, and it is real: Storage Manager 1.0.0-01026, published October 8, 2025, fixed a volume that would not mount after a DSM update if it had already had an SSD cache missing event on DSM 7.2.1. A reboot with a write-back cache that has not flushed is the cache page. Read that one before you restart a box that has an M.2 cache. For a plain SHR or RAID pool with a failed hard drive and no cache, the hazard we will actually claim is the one in Synology's own crash causes: another drive drops, or the shutdown is not clean, and the volume that was Degraded comes back Crashed.
The pool is Degraded and an update is waiting, or it already ran and the volume is Crashed. Stop. If the shares still open, copy the files off before anyone restarts the NAS, clicks Repair, or reinstalls DSM.
Copy the files off. Repair is a later job.
If File Station still opens the shares, copy what you care about to another computer or another disk. That is the backup the pre-update article asks for, taken while the volume is the thing Synology still calls accessible. Open a few of the copied files. A copy you have not opened is a progress bar. Their RAID 5 description says read and write performance is severely impacted while the array is degraded, because the missing drive is reconstructed from the others. The copy is that read. If it starts failing, or a surviving disk starts clicking, stop and power the NAS off. Pushing the rest of the copy is how the last members get spent.
Then find the drive, on paper. Storage Manager > HDD/SSD. The current help's status list includes Healthy, Critical (critical errors, read-only mode, or an SSD at its endurance limit — they say replace that drive immediately), and System Partition Failed. Replace-immediately is their line for that drive. If this pool is the only copy, the copy comes before the swap. Select the drive and open Health Info for power-on time and temperature. Photograph the storage-pool page and the drive list, including which bay is which. Locate Drive, on that same HDD/SSD page, changes the bay LED so you are looking at the slot DSM means. Write the slot number on the tray before anything comes out.
Synology's repair steps, when you get to them, are specific. Remove the defective drive and replace it with a healthy one. All existing data on the replacement is erased. If the NAS does not support hot-swap, power it off before you remove or install a drive. Back on Storage Manager > Storage, select the Degraded pool, open the upper-right icon, and choose Repair. The Repair option only appears when the pool is Degraded, and only for pools with data protection: RAID 1, RAID 5, RAID 6, RAID 10, RAID F1, and SHR of at least two drives.
Fast Repair is enabled by default. It skips unused space so the used part of the pool is protected again sooner. It is still a repair of the disks that are left. Leave the checkbox where it is while you are copying. Auto Repair is off by default. When it is on, inserting the replacement in the same slot starts the repair without the manual steps. It is not supported on SHR, and it exists only on models that support a RAID Group. A hot spare is separate. If a drive is assigned as a hot spare to protect the pool, the repair article says that spare repairs a degraded pool automatically. Do not assign a spare, and do not turn Auto Repair on, so a rebuild starts while the copy is still running. If a repair is already underway, do not start a DSM update on top of it. The pre-update article lists repairing a volume as work to avoid during an update.
Repair is a rebuild. The rebuild page says that is ordinary maintenance when one drive has failed, the array is still online, and every remaining member is healthy. A degraded pool you have been ignoring, or a second disk that is slow, clicking, or already Critical, is the case that sentence does not cover. Two members down on RAID 5 or SHR with one disk of redundancy is past what the array can rebuild. Do not pull a second drive "to read the serial in a PC." Deactivate is refused at maximum fault tolerance because the pool would crash. Pulling the drive anyway gets you there without the dialog.
The DSM update still waits until the pool is Healthy, even after the copy. The copy protects you. The update still restarts, and it still writes the system partition on a disk you have not replaced. Healthy, then the patch. If the surviving disks are not something you would rebuild from, the patch waits and the set goes to a lab.
If the update already ran
Stop. The volume you can still read is copied, and then nothing else writes. The volume you cannot read is left alone.
If DSM comes up and File Station can still read the data, the volume-crash article's readable scenario says not to power the system off, and to back up to a computer on the local network. Do that. The next steps in that scenario are remove the storage pool, run a memory test, create a new pool and volume, and restore. Removing the pool is a delete. It belongs after a copy you have already checked, and it is a bad idea on the original disks if the copy is short. You are allowed to stop after the copy.
If DSM comes up and File Station cannot read the data, the same article says to contact a data-rescue company. That is the stop. Do not click Repair. On a Crashed storage pool, Synology's repair article already says you can no longer repair it yourself. Repair on a crashed volume is the write covered on the Volume Crashed page. Do not remove the pool and create a new one on these disks so the NAS "works again."
If the NAS will not power on, or it powers on and DSM never comes back, scenario 1 of that article says to fix the drive failure and retrieve the data from the drives. A reset-pinhole reinstall is a different article. For a crashed system partition, Synology says back up, then use Mode 2 to reset and reinstall DSM. The partition article says reinstalling the operating system does not recreate the partitions. It removes system data from the system partition. Their insufficient-capacity article describes a factory reset separately: it erases all data and creates a larger system partition. Neither one mounts a volume that crashed on the way back from an update. Both of them assume a backup you make before you reset. If the volume is already unreadable, you do not have that backup. Leave the reset hole alone.
Do not hunt for an older .pat file. The System Update help says updates are irreversible. The September 17, 2026 pre-update article says you cannot roll back. The 7.4 and 7.4.1 notes repeat that a downgrade is unavailable after those installs. A downgrade is another install and another restart on the disks you are trying to keep.
Leave the drives in their slots until they are labeled. Slot order is part of the set. If a drive was pulled by mistake, the volume-crash article says to put that drive back immediately. On DSM 7, Storage Manager > Storage can then Online Assemble, without a restart, once the original drives are detected. The assemble help says a Crashed or Missing pool can be assembled when enough drives are installed and the serial numbers match Required Drive Info, and the status then changes to Can be assembled. That is the accidental-removal case. A drive that dropped because it failed is a different failure. Put back the drive that came out of that slot. If you did not pull a drive, leave Online Assemble alone.
What to do right now
- Do not start the update. Not a major DSM update, not a minor one, not Manual DSM Update, not Storage Manager, not Hybrid Share, not Action > Firmware Update. If a drive is clicking or the NAS is already down after an update, skip the settings and go to the last step.
- If the shares still open, copy them to a different disk. Photograph Storage Manager: pool status, RAID or SHR type, the HDD/SSD list, bay numbers, and the exact update text. Locate Drive if you need the LED to match a bay. Write the slot numbers down.
- If DSM is still up and a drive is not failing under your hand, stop a scheduled install from running tonight. On a 2024-or-earlier model, "Notify me and let me decide whether to install the new update" is the setting that does not install. On a 2025-or-later model, the postpone link on an important-update notification is the control Synology documents, once, for up to 28 days. The copy still comes before that click.
- Repair only if you are still Degraded, you know which single drive failed, and the others are Healthy — and only after the copy. Synology's order is replace that drive, then Repair. No hot-swap support means power off before the swap. Do not enable Auto Repair. Do not pull a second disk. Do not update DSM between the copy and a finished, Healthy pool.
- If the volume is Crashed, File Station cannot read, the NAS will not come back, a second drive looks bad, or someone already clicked Repair, reinstalled DSM, or reordered the bays, stop. Power off a clicking unit. Label every slot. Keep every disk, including the one that failed and any disk you already inserted. How to ship a failed drive. If the volume was encrypted, bring the key. The key unlocks the volume. It does not rebuild a member the update already lost.
How a lab handles it
We do not install DSM on your NAS to see if the pool comes back. We do not click Repair, Repair System Partition, Online Assemble, or Mode 2 reset on the original disks. We do not downgrade them, and we do not create a new pool on them.
Each member is imaged write-blocked, as far as it will read, including the drive Storage Manager already called defective. SHR or mdadm, then LVM, then Btrfs or ext4, is reassembled from the copies. A wrong guess about which disk failed costs a copy. An update, a repair, or a reinstall on the originals writes the disks you still have. If the shares were readable, the copy you made before they stopped is the cleanest version of those files, and it should exist before the drives are asked to do anything else.
The public case log has no job where a DSM update was run against a degraded pool. We will not invent a case ID or an outcome for one. The published Synology set is DDR-2026-0003: a four-drive RAID 5, two members failed, volume inaccessible, EXT3/4, nothing rebuilt in the NAS. Full recovery on that job. That is what happened on that set. It was already past a degraded rebuild, and it was not an update. It is not a rate, and it is not a promise about a Btrfs volume that crashed after an update. We don't advertise a success rate, and we can't promise a turnaround from a DSM version number.
Call when the copy stops working, the volume is Crashed, the NAS does not come back, or a second disk is in question. The evaluation is at Desert Data Recovery, in the Phoenix area. The number on this page is (602) 686-2622. For the set itself, see RAID data recovery.
DSM update on a degraded pool — FAQ
The pool says Degraded and DSM is offering an update. Will the update fix the drive?
Is a minor update, or a Storage Manager or Hybrid Share update, a different risk?
The update setting is on automatic. Can the NAS install this by itself?
Does the update write every disk in the pool?
The update already finished and the pool says Crashed, or the NAS will not boot. What do I leave alone?
I already copied the important files. Is Repair safe now?
Should I run the file-system check DSM is prompting, so the update will proceed?
Is there a DSM-update case in the public log?
A Degraded pool is still serving the files, and a DSM update restarts the box that is serving them. Copy the data off. Leave the update, the package update, and Repair until the drives are Healthy — or until someone is working from images. If the update already ran and the volume is Crashed or the NAS will not come back, stop and start with a free evaluation.
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