Limitations for independent disks in VMware virtual machines. Not backed up using vStorage API

Limitations for independent disks in VMware virtual machines. Not backed up using vStorage API

Article: 100024362
Last Published: 2018-09-06
Ratings: 3 3
Product(s): NetBackup

Problem

Limitations for independent disks in VMware virtual machines. Not backed up using vStorage API.

VMware does not support snapshots of independent disks in a virtual machine, both persistent and non-persistent.  As a result these disks are not backed up.  On restore these disks are recreated, but with no content.

Error Message

none

Cause

Notes from VMware documentation pertaining to independent disks and snapshots:

Working with snapshots - http://kb.vmware.com/kb/1009402

Note: Virtual disks which are configured to be independent-persistent cannot use snapshots.
 

VMware vSphere Administration Guide - http://www.vmware.com/pdf/vsphere4/r41/vsp_41_vm_admin_guide.pdf

Independent disks are not affected by snapshots.

Introduction to VMware vSphere - http://www.vmware.com/pdf/vsphere4/r40/vsp_40_intro_vs.pdf


independent disk:   A type of virtual disk that is not affected by snapshots. You can configure independent disks in persistent and nonpersistent modes. See also nonpersistent mode, persistent mode

nonpersistent mode:  A disk mode in which all disk writes issued by software running inside a virtual machine appear to be written to the independent disk. In fact, they are discarded after the virtual machine is powered off. As a result, a virtual disk or physical disk in independent-nonpersistent mode is not modified by activity in the virtual machine. See also disk mode, persistent mode.

persistent mode:  A disk mode in which all disk writes issued by software running inside a virtual machine are immediately and permanently written to a virtual disk that is configured as an independent disk. As a result, a virtual disk or physical disk in independent-persistent mode behaves like a conventional disk drive on a physical computer. See also disk mode, nonpersistent mode.

snapshot:  A reproduction of the virtual machine just as it was when you took the snapshot, including the state of the data on all the virtual machine’s disks and the virtual machine’s power state (on, off, or suspended). You can take a snapshot when a virtual machine is powered on, powered off, or suspended. See also independent disk.

Notes from NetBackup 7.1  for VMware Administration Guide pertaining to independent disks:

Page 20:

independent disk:  A virtual disk that cannot be captured with a snapshot. An independent disk can be configured as either persistent or temporary.

Note: NetBackup for VMware cannot back up the data on an independent disk. The backup succeeds but the backup image contains no data for the independent disk. If you restore the disk from the backup, the independent disk is restored to its original allocation size but contains no data. For example, the Windows swap file can reside on an independent disk, and is consequently not included in the virtual machine backup.

Page 28:   VMware notes and restrictions

NetBackup for VMware cannot back up the data on an independent disk, because an independent disk cannot be captured with a snapshot. The backup succeeds but the backup image contains no data for the independent disk.

Note, even in VCB we did not capture independent disks.  This used to cause the backups to fail with Status 156.  We now will not fail with Status 156 as there may be other disks that can be protected (non-independent disks).

Page 160:    For VCB 1.5 update 2 and for vStorage, the RDM is ignored (not backed up) and any independent disk is recreated but empty.

Page 169:  NetBackup for VMware skips the vmdk files that are marked as independent. Make sure that the databases and transaction logs are not stored on independent disks.
 

Solution

Three options:

1.  If the data on the independent disks is needed for restore at any time, they should not be flagged as independent, allowing them to be backuped up via vStorage API and restored along with a fullvm restore, or as individual files.

2.  Alternately, you could backup up the independent disks using a NetBackup client installed in the virtual machine.  This would allow for normal single-file restores using non-vStorage NetBackup client methods.  This could be combined with first doing a full virtual machine restore using vStorage API, then doing a single file restore of the data on the independent disks using NetBackup client.

3.  Finally, assuming the original virtual machine is intact, the full virtual machine could be restored to an alternate location in vSphere. 

You would end up with:

Original location:   non-independent disks and independent disks still intact
Alternate location:  restored non-independent disks and zeroed out independent disks.

At this point the VMware administrator could move the non-persistent vmdk files to the original VM if you wanted too.  Additional tweaking on the original VM may be needed.  For example if the VMDK was a different name, the VMX file will not know about it.  They would proabably have to power off the original, remove the original disk, add the restored disks, etc.  The VMware administrators should know the steps involved.

Note this last option does not allow for restoring data from the independent disks.  It assumes the data is still available in the original virtual machine.

 

 

Applies To

NetBackup 7.0 and 7.1 backing up VMware ESX 3.5 and vSphere virtual machines.

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