What is LUN re-signature and what is it’s importance


When a LUN is presented to ESX host, it get’s a signature. This signature is in the form of UUID. When you take a snapshot of LUN, the exact UUID is copied in the snapshot. So when you wish to restore the snapshot in case of DR, in ESX4.0 you are given a option to re-signature the disk i.e. to assign a new signature to the disk or assign the existing signature

Remember you cannot mount datastore whose signature collides with existing signature. You either have to give new signature to datastore or unmount the exisiting datastore. There are pros and cons

So what happens if you decide to re-signature the copy of  datastore

  • New signature is assigned to datastore
  • It looks distinct than the existing datastore as it assigns new name it as snap-<snapID>-<oldlabel>
  • But most important concern, once you re-signature, you will have to register vmx file, vmsd and vmsn file

In general in production scenario, snapshot is taken for every lun and placed in DR site. So when production fails, this lun is mounted in the production site without resignaturing and all your vm’s are up in a 5-10 minutes time

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2 comments on “What is LUN re-signature and what is it’s importance

  1. Pingback: 2010 in review (Thank you for this) « Designing vSphere

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