Citrix has announced the availability of the “Creedence” tech preview of the next version of XenServer, building on the open-source Xen Project’s Creedence alpha.4 release. The biggest change in Creedence is the move to an all 64-bit implementation. While the Xen hypervisor has always been 64-bit and can run both 32 and 64-bit guest operating systems, the XenServer control domain, dom0, has not. Dom0 is where the management tasks run, and more importantly here, it is where the physical hardware is controlled. Moving to a fully 64-bit implementation will enable significant performance and scalability improvements as well as important changes to hardware support.
A 64-bit control domain means that the current limit on the number of PCI devices that can be attached per host will increase, providing the opportunity to grow the number of virtual NICs supported, thus adding significantly to configuration flexibility. At the same time, this allows PCI devices with only 64-bit drivers, such as many SSD drives, to be used for the first time. Of import to XenDesktop users, the 64-bit control domain means that Creedence can support vGPUs on physical GPUs mapped above the 4-gigabyte boundary in the system address space. This in turn means that it can run significantly more GPUs than were possible previously. XenServer 6.2 currently supports up to sixty-four vGPUs or eight physical GPUs per host. Citrix has not yet confirmed the practical limit for the number of GPUs Creedence will run, saying only that “moving to a 64-bit platform will allow us to significantly increase these limits.”
The full list of new features in Creedence is as follows:
- 64-bit dom0
- Adoption of the Linux 3.10 kernel
- TRIM and UNMAP for better storage reclamation on SSD
- Reintroduction of workload balancing and the Distributed Virtual Switch Controller (DVSC) that was dropped from XenServer in version 6.2
- 32-bit to 64-bit VM migration
- Storage migration from XenServer 6.2 and prior
- Newly supported guests:
- CentOS/RHEL 5.1.0 and 6.5
- SLES11 SP3
- Ubuntu 14.04 LTS support
- Support for latest-generation servers, including processor hardware refresh:
- Intel Ivy Bridge-EX
- Intel Haswell EP
- Performance improvements
- Support for Generic Receive Offload (GRO) for increased network performance (improved networking throughput to allow greater numbers of VMs to run effectively per host)
- Support for tapdisk3 (up to 100% increase in read performance)
- Boot storm handling improvements by using read caching
- Read caching for file-based SRs
- Open virtual switch 2.1.1
- Decouple device driver versions from dom0 kernel build versions
- Improved XenCenter logs and alerts
- Cost and Manageability
- Microsoft System Center integration
- XenCenter installer improvements, including a slimmed-down .NET installation (payoff on subsequent reduction in hotfix size)
- Graceful handling of out-of-storage conditions
- Improved IPv6 guest support.
Citrix is already promoting the performance improvement that read caching can deliver for VDI workloads. Steve Wilson shared this graph on his blog post Ramping Up XenServer!
The company hasn’t yet decided whether Creedence will be christened version 6.5 or 7.0, or when it will be released.