Override default iSCSI parameters InitialR2T MaxOutstandingR2T in CORE

Hi TrueNAS Experts,

Short Version:

How can we change these two iSCSI parameters?

  • MaxOutstandingR2T to 16 or 32
  • InitialR2T to NO

Current Negotiated iSCSI Parameters:

yaml

KopierenBearbeiten

HeaderDigest: None  
DataDigest: None  
MaxRecvDataSegmentLength: 262144  
MaxXmitDataSegmentLength: 262144  
FirstBurstLength: 262144  
MaxBurstLength: 1048576  
ImmediateData: Yes  
InitialR2T: Yes  
MaxOutstandingR2T: 1  

These settings seem suboptimal and could be improved.


Details:

Setup: oVirt KVM/QEMU hypervisor with multiple nodes using TrueNAS as storage via iSCSI.

We’re currently running TrueNAS-12.0-U2 (planning to upgrade in the next months) and want to adjust some iSCSI parameters.

  • According to older documentation, TrueNAS allows MaxOutstandingR2T values between 0-255.
  • InitialR2T is currently set to Yes.
  • All our iSCSI connections negotiate to:
    • InitialR2T: Yes
    • MaxOutstandingR2T: 1

Even though our CentOS initiators are configured with MaxOutstandingR2T: 16, TrueNAS seems to ignore it.


What We’ve Tried:

  1. Editing /etc/ctl.conf → gets overwritten by database values.
  2. Checked the TrueNAS database (midclt call iscsi.extent.query | jq) → No related fields found.

Example extent entry from TrueNAS:

json

KopierenBearbeiten

{
  "id": 22,
  "name": "Extent_ovirt_default_DC05",
  "serial": "309c239e05b8021",
  "type": "FILE",
  "path": "/mnt/hdd_pool05/dataset_ovirt_DC05/Extent_File_DC05",
  "filesize": "2199023256064",
  "blocksize": 512,
  "pblocksize": false,
  "avail_threshold": null,
  "comment": "",
  "naa": "0x6589cfc0000007b10e94cd92661bc0c6",
  "insecure_tpc": true,
  "xen": false,
  "rpm": "SSD",
  "ro": false,
  "enabled": true,
  "vendor": "TrueNAS",
  "disk": null,
  "locked": false
}

Unfortunately, our oVirt infrastructure enforces a 512 block size.


Questions:

  1. Where does TrueNAS store these iSCSI negotiation parameters, and can they be modified persistently?
  2. Will this be configurable in TrueNAS CORE 13 via the Web UI?
  3. Is there any way to force MaxOutstandingR2T >1 on the TrueNAS side?

Any insights would be greatly appreciated!

Thanks in advance!
Best regards,
Raphael

You should be looking at TrueNAS Scale. Core is essentially EOL and only receiving security updates and a few other fixes. I don’t know how long you will get security updates unless your on Enterprise version.

Development of improvements are focused on TrueNAS Scale

Thanks for the fast response.

Yes planning to switch to TrueNAS SCALE in our new datacenter mid2end 2025. But for now (never change a running production system) we stick to CORE.

But maybe it was never possible to change these values. Even they seem to be arround more than 10+ years at least on my research.

  • MaxOutstandingR2T
  • InitialR2T

Kind if odd, because i have seen it in some forum posts, but maybe this was part of the ‘xen’ only features.

Kind regards,
Raphael