# DRBD 9.3.0: resync may stall in a 3-node cluster leading to blocked I/O when promoting an Inconsistent node

**URL:** <https://forums.linbit.com/t/drbd-9-3-0-resync-may-stall-in-a-3-node-cluster-leading-to-blocked-i-o-when-promoting-an-inconsistent-node/1169>\
**Category:** DRBD\
**Tags:** drbd\
**Created:** [March 8, 2026, 3:59am UTC](https://forums.linbit.com/t/drbd-9-3-0-resync-may-stall-in-a-3-node-cluster-leading-to-blocked-i-o-when-promoting-an-inconsistent-node/1169 "2026-03-08T03:59:23Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![buaafanrui](https://avatars.discourse-cdn.com/v4/letter/b/9e8a1a/32.png) [@buaafanrui](https://forums.linbit.com/u/buaafanrui)\
**Post date:** [March 8, 2026, 3:59am UTC](https://forums.linbit.com/t/drbd-9-3-0-resync-may-stall-in-a-3-node-cluster-leading-to-blocked-i-o-when-promoting-an-inconsistent-node/1169/1 "2026-03-08T03:59:23Z")

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# Environment

- DRBD version: **9.3.0**

- Cluster size: **3 diskful nodes**

- Resource: **r1**

- Nodes: **drbd1, drbd2, drbd3**

- Protocol: **C**

- Single primary (no dual-primary)

* * *

# Problem Description

In a 3-node DRBD cluster we occasionally encounter a situation where **resynchronization stalls and all write I/O to the mounted filesystem blocks indefinitely**.

When this happens:

- resync progress stops

- writes to the mounted filesystem hang

- the filesystem cannot be unmounted (`umount` blocks)

- DRBD status shows `peer` / `dependency` suspended states between nodes

Restarting DRBD on one node (`drbdadm down/up`) causes the resync topology to change and the system recovers.

* * *

# Reproduction Scenario

The issue can be reproduced with the following sequence.

Nodes involved:

```auto
drbd1
drbd2
drbd3

```

Initial state: all nodes are **UpToDate**.

* * *

### Step 1

Promote **drbd3** to Primary and mount the filesystem.

* * *

### Step 2

Disconnect the network between **drbd3** and **drbd2**.

* * *

### Step 3

Write data on **drbd3**.

Result:

```auto
drbd2 becomes Outdated

```

* * *

### Step 4

Restore the network between **drbd3** and **drbd2**.

Result:

```auto
drbd3 → drbd2 resync starts

```

* * *

### Step 5

Promote **drbd2** to Primary and mount the filesystem.

Then disconnect the network between **drbd2** and **drbd3**.

Because **drbd2** is now Primary and receives writes:

```auto
drbd3 becomes Outdated

```

* * *

### Step 6

Restore the network between **drbd2** and **drbd3**.

Current state becomes:

```auto
drbd1 : UpToDate
drbd2 : Inconsistent (Primary)
drbd3 : Outdated

```

DRBD chooses the following resync direction:

```auto
drbd3 → drbd2

```

* * *

### Step 7

Write data on **drbd2**.

At this point the problem occurs.

* * *

# Observed Behavior

1. The resync from **drbd3 → drbd2** stalls (no further progress).

2. The filesystem cannot be unmounted.

DRBD status shows the following relationship:

```auto
drbd1 → drbd2
    drbd1: resync-suspended: peer
    drbd2: resync-suspended: dependency

```

This suggests that:

- `drbd1 → drbd2` resync is waiting for another resync to complete

- `drbd2 ← drbd3` is expected to complete first

However:

```auto
drbd3 → drbd2 resync shows "suspended: no"
but makes no progress.

```

As a result, the whole system appears to be stuck.

* * *

# Recovery

If we restart DRBD on **drbd3** :

```auto
drbdadm down r1
drbdadm up r1

```

The resync topology changes to:

```auto
drbd1 → drbd2
drbd1 → drbd3

```

Both nodes resync from **drbd1** , and the cluster returns to normal operation.

* * *

# Question

Is this behavior expected in DRBD 9.3.0 when a node that is still **Inconsistent** is promoted to Primary and receives writes?

Or could this indicate a **resync scheduling issue** where DRBD chooses a suboptimal sync source (Outdated node) and the resync pipeline becomes stalled?

Any guidance on how to avoid or diagnose this situation would be appreciated.

 ![resync-stuck](https://canada1.discourse-cdn.com/flex003/uploads/linbit/original/1X/7291192b8fa18ccfdef91cac70a2a00d895701a8.png)

---

<div class="post-metadata">

**Author:** ![buaafanrui](https://avatars.discourse-cdn.com/v4/letter/b/9e8a1a/32.png) [@buaafanrui](https://forums.linbit.com/u/buaafanrui)\
**Post date:** [March 8, 2026, 4:04am UTC](https://forums.linbit.com/t/drbd-9-3-0-resync-may-stall-in-a-3-node-cluster-leading-to-blocked-i-o-when-promoting-an-inconsistent-node/1169/2 "2026-03-08T04:04:36Z")

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![drbd1-2-3](https://canada1.discourse-cdn.com/flex003/uploads/linbit/original/1X/6e572b582b99bf3906f60bd1557464d6d9f83f77.png)

this is drbdadm status results