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VMFS Recovery: SFTP or SSH network connection error

Our customers often write us that establishing remote connection to ESX server via SFTP results in following error:

Failed to establish SFTP connection error code 103. - The semaphore cannot be set again

We have investigated this issue and discovered that this problem may appear at the ESX 4.x versions that doesn't have SFTP support. This is network error message, and normally it appears when number of connections from one client exceeds predefined limit at server, however ESX 4.x doesn't have proper SFTP support which is required to gain direct disk access via network. If you see such error, you have following options:

  • close other programs that may have already established connections to ESX such as Putty or other SFTP client. Try to reconnect when resources are free.

  • upgrade your ESX to 5.0+ version to access it via SSH,

  • access VMFS disk(s) or drive images directly using some dedicated, stand alone, physical Windows PC.

Actually we recommend everyone to use last option, it could require more effort, however you will reduce recovery time a lot.

Please note: accessing VMFS via network protocols like SSH or SFTP severely reduce performance. Our test configuration achieves scan speed of approx 340Gb per hour for local disk access for simgle HDD. Compare it with 1.5Gb per hour via SFTP/SSH on a binded 2*1Gbit LAN connection.

If you would like to obtain more information about this problem you may be interested to check the following links: MS TechNet description, MSDN error codes, similar problem explained with VmWare Virtual Desktop Manager.