Windows Server · high · Failover clustering & Hyper-V

Cluster Shared Volume in redirected access — everything slows down

A node has lost its direct path to the storage and is sending all its I/O over the cluster network via the coordinator node.

What you see

Virtual machines on one node become slow while the same machines run normally elsewhere. The volume shows redirected access in the cluster console.

What is actually wrong

A lost storage path on that node, a backup product holding a snapshot, or a filter driver that forces redirection.

Codes and articles

redirected accessEvent 5121Event 5125Event 5142CSV redirectedFile System Redirected

Fixes (2)

Restore the node's direct path to the storage

Elevated PowerShell on the affected node60 minutesmedium riskreversible

One node is redirected.

Confirm which volumes and nodes are affected.
PowerShell
```
Get-ClusterSharedVolume | Format-Table Name,State,OwnerNodeGet-ClusterSharedVolumeState | Format-Table Name,Node,StateInfo,VolumeFriendlyName,RedirectedIOReason
```
RedirectedIOReason names the cause directly — NoDiskConnectivity, UserRequest, BlockRedirectedIOdueToFileSystemFilter and so on. That one field decides which of the fixes applies.

For NoDiskConnectivity, check the storage paths on that node.

PowerShell

Get-Disk | Format-Table Number,FriendlyName,OperationalStatus,BusTypempclaim -s -dGet-InitiatorPort | Format-Table NodeAddress,ConnectionType,OperationalStatus

Check the SAN zoning and the HBA or iSCSI sessions from that node specifically.

Turn redirection off once the path is restored.

PowerShell

Get-ClusterSharedVolume 'Cluster Disk 1' | Set-ClusterSharedVolumeState -State Normal

If it was set manually for maintenance and forgotten, that is the whole cause.
PowerShell
```
Get-ClusterSharedVolumeState | Where-Object StateInfo -ne 'Direct' | Format-List
```

Confirm it workedEvery node reports Direct I/O for the volume.

PowerShell

Get-ClusterSharedVolumeState | Format-Table Name,Node,StateInfo

If you need to undo itSet-ClusterSharedVolumeState -State FileSystemRedirected restores redirection if needed for maintenance.

Find the filter driver forcing redirection

Elevated PowerShell60 minutesmedium riskreversible

Every node is redirected.

List the filter drivers attached to the CSV volume.
PowerShell
```
fltmc filtersfltmc instances -v C:\ClusterStorage\Volume1
```
A backup agent or antivirus filter that is not CSV-aware forces the whole volume into redirected mode for as long as it is attached. The list names it in one command.

Check whether a backup is running or a snapshot has been left behind.

PowerShell

vssadmin list shadowsGet-ClusterSharedVolumeState | Format-Table Name,Node,StateInfo,RedirectedIOReason

Remove an orphaned snapshot if a backup failed part way.
PowerShell
```
vssadmin list shadows /for=C:\ClusterStorage\Volume1
```
Add the CSV paths to the antivirus exclusions along with the Hyper-V process and file types — this is a documented requirement, not a performance tweak.
PowerShell
```
Get-MpPreference | Select-Object -ExpandProperty ExclusionPath
```
Update the backup agent to a version that supports CSV direct I/O, or schedule its work in a maintenance window.

Confirm it workedState returns to Direct on every node and virtual machine performance recovers.

PowerShell

Get-ClusterSharedVolumeState | Format-Table Name,Node,StateInfo

If you need to undo itExclusions can be removed; the backup agent version can be rolled back.

Where this stops. This write-up was written and checked by hand. It says what each step changes, how to confirm it worked and how to reverse it, and anything destructive is flagged before you reach it. If it does not match what your machine is doing, search the Support Centre for the exact code or message — and when something needs a person, get in touch.