Longhorn UI · Developed by us

Choose how many NVMe-TCP I/O queues a v2 volume uses

A v2 volume opens one I/O queue per CPU core by default, and each queue costs memory on the storage node. Longhorn can now set the count per volume, so we added the field to Create Volume and show the value in the volume details.

In review PR 1098 ↗ Issue 13735 ↗ Backend issue 13706 ↗ Detailed review ↗

What changes for the user

Create Volume has a new NVMe-TCP IO Queues field right under Frontend. It only appears for v2 volumes that use the Block Device frontend.
The default is 0, which means "use the global setting". The help icon shows the current global value and says that the value applies on the next attach.
Only 0 to 128 is accepted. Anything else shows an error.
The volume details page shows the value under Frontend.
Clone Volume and Bulk Clone keep the value of the source volume.

The flow

A new field in Create Volume

Pick the v2 data engine with the Block Device frontend, and the queue field appears under Frontend, set to 0.

Create Volume before and after: the NVMe-TCP IO Queues field appears under Frontend — Before, every v2 volume used the global setting. Now each volume can set its own number. It sits in the same place as UBLK's queue fields.

The help text explains the number

The tooltip gives the full name, the current global value, when the value applies, and the CPU limit.

Tooltip on the NVMe-TCP IO Queues field — The node never creates more queues than it has CPU cores, so this setting can only lower the count.

Out-of-range values are rejected

Typing 200 shows "Must be between 0 and 128". When the field loses focus, the value is clamped.

Validation error for 200 — The same 0–128 range that the backend accepts.

Other frontends don't show the field

UBLK keeps its own two queue fields, and v1 volumes and NVMf show neither.

Create Volume with the UBLK frontend: no NVMe-TCP field — Only Block Device connects over NVMe-TCP, so the field is hidden for the others and nothing is sent.

Volume details show the value

A v2 Block Device volume now shows its queue count under Frontend, with an info icon that explains 0.

Volume details before and after: NVMe-TCP IO Queues: 1 — This volume was created with 1 queue. Before, the details page had no way to show it.

Video (optional)

0:00 Before · 0:15 After

Notes

The count can only be set when the volume is created. The backend has no way to change it on an existing volume.
Details show the configured value. A volume left at 0 shows 0, not the global value it ends up with.
The global default is already on the Settings page, so that page did not change.