Linux on Hyper-V: TimeSync

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So why do I think TimeSync is more important than SMP for Linux on Hyper-V?

First, let me recap… last week Microsoft released a beta version of updates to the Linux Integration Services (ISs / Integration Components / ICs). 

This release of the ISs includes three new features customers have been asking for:

  • SMP (multiprocessor) support
  • Time Sync
  • Shutdown Integration

Most enterprise have lots of Windows – on the desktop as well as on servers in the data center and branch offices.  I understand that some times (gasp) a few Linux servers may sneak into an enterprise because of business requirements (application only ships on Linux, for example).  For primarily Windows enterprises, there may be a requirement to support a few Linux servers here and there (yes there are organizations with more Linux than that…they should look at Hyper-V too!).  Typically, these are not high-performance systems, often just one-offs. The question I often ask administrators about those Linux systems is, “do you back them up?”  Often the answer is, “I don’t know”  (that answer means no to me!).

Encapsulating Linux in a VM on Hyper-V makes backup and recovery a snap…literally.  I’ve detailed it in earlier posts… you can use DPM, Windows Server Backup (WSB), or the diskshadow command to easily backup and restore Hyper-V virtual machines INCLUDING Linux!   ntp

One challenge with Linux had been the lost seconds on in the Linux VM clock when the VM is “frozen” for backup (not an issue for most Windows VMs because of VSS backup integration).  When a host backup was invoked for a Linux (or non-backup aware) VM, the virtual machines state would be saved to disk to facilitate a host-based snapshot.  During the  seconds it would take to create the snap, the VM would not be able to track time (count ticks), and the clock would typically be slow equal to the down time.  This could be corrected with NTP and the proper slew settings, but it was a hassle (the picture to the right). 
Why couldn’t Linux just get the time from Hyper-V like Windows VMs?  
With the new Integration Services, Linux virtual machines can!  

TimeSync means that you don’t have to hassle with configure network-based time sync for your Linux VMs on Hyper-V…they can get the correct time from the host!  Time is automatically updated (if you install the new Integration Services) on your Linux VMs even if they are “saved” for a while.  I just did this in my lab a bunch of times with a bunch of Linux VMs, and it worked great!

The new TimeSync Integration Service for Linux makes it ever easier for administrators to backup and restore non-Windows VMs on Hyper-V without impacting business applications.