Knowledge Base

Backing up from inside a virtual machine is done in the same way you back up a physical machine. Backing up from outside a virtual machine consists of copying the various files that constitute a virtual machine.

Some things you should keep in mind when backing up virtual machine files:

• Virtual machines comprise several files, which are normally stored on two different volumes.

  • The large files belonging to a virtual machine are usually stored on a VMFS volume. These include the virtual disk (.dsk), redo logs (.REDO), and suspended state files (.vmss).
  • The service console file system contains the virtual machine's configuration file and other small files belonging to the virtual machine. You can find the path to the configuration file from the VMware Management Interface by mousing over the virtual machine's display name on the Status tab. To back up the complete virtual machine, you need to include all the files in the same directory as the configuration file.
  
  
  

• ESX Server uses a proprietary file system called VMFS. VMFS is designed for high speed access and large file sizes. ESX Server virtual disks are always preallocated to their full size; they do not start out as small files and grow as information is written to them. Also, they are not divided into 2GB extents.

  Some file systems (for example, VFAT or EXT2) cannot store files larger than 2GB. If you move an ESX Server virtual disk to such a file system, you must convert the disk to a multi-file format understood by GSX Server and Workstation. Whereas an ESX Server system always uses a single file for a virtual disk, GSX Server and Workstation systems may use more than one file to represent a single virtual disk. These files grow to 2GB each, allowing them to be stored on almost any file system.

• Some file utility programs can also have problems with files larger than 2GB. SCP and FTP, however, are capable of handling files larger than 2GB. These tools can safely be used to move ESX Server virtual disks to other VMFS volumes, or to back them up on file systems capable of handling files over 2GB. However, be sure to use binary mode when transferring virtual disks with FTP.

• If you want to back up ESX Server virtual disks larger than 2GB to a file system that limits file size to 2GB, you can use vmkfstools or the VMware Management Interface to export them from the VMFS volume to another file system. When you export a virtual disk from an ESX Server system, it is converted from the format used by ESX Server to the multiple file format used by GSX Server and Workstation. In order to restore a virtual disk for use with an ESX Server system, you need to convert it back to ESX Server format with an import operation using vmkfstools or the VMware Management Interface. Refer to www.vmware.com/support/kb/enduser/std_adp.php?p_faqid=900 for more information on using these tools to move virtual disks.