SIRIS, ALTO, and NAS: iSCSI connection fails with "Log On to Target" error



When you try to establish a new connection from your workstation to an iSCSI share on the Datto appliance, you see an alert box titled, "Log On to Target," with either an, "Authentication Failure," or, "Initiator CHAP secret given is invalid. Maximum size of CHAP secret is 12 bytes ifIPSec is not used," error.

The wording of this error may differ depending on your OS. The examples in this article are from Windows 10.


  • Datto SIRIS
  • Datto Alto
  • Datto NAS
  • Datto IRIS 3.89
  • Microsoft Windows 10


After the Datto software update to IRIS 3.89, CHAP Mutual authentication requires that the CHAP secret and CHAP Mutual secret do not match. If you are using CHAP Mutual Authentication and your two CHAP authentication secrets match, you will need to change one of them.


Figures 1 and 2 show the errors as they appear in Windows 10.

logon1.pngFigure 1: Authenticate failure (click to enlarge)

logon2.pngFigure 2: Initiator CHAP secret given is invalid (click to enlarge)

1. From the Datto device GUI, navigate to FILE SHARE → Network Attached Storage 

fileshare.pngFigure 3: Network Attached Storage (click to enlarge)

2. Click Configure Share Settings for the iSCSI share you need to connect.

configure.pngFigure 4 Configure Share Settings (click to enlarge)

3. In the CHAP Authentication box, set the CHAP Secret and Mutual CHAP Secret to two different passwords. You can click the eye icon to make the password visible.

chapmatch.pngFigure 5: CHAP Authentication (click to enlarge)

4. Click APPLY.    

5. Update the iSCSI connection information on your connecting machines to reflect the new passwords.

You should now be able to connect to the share. If the connection still fails, contact Datto Technical Support.

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