The December 2010 and February 2011 columns for ;login: are now out. This two-parter compares Solaris, RHEL, and AIX. Probably controversial! Feedback welcome.
Have a look:
December 2010 ;login: Magazine: Comparing Solaris, RHEL, and AIX Part 1.
February 2011 ;login: Magazine: Comparing Solaris, RHEL, and AIX Part 2 – virtualization.
Peter,
I’ve just finished reading your articles and I was glad to see this comparison of the data center operating system market. I’ve always been a fan of your articles and pass them on to as many folks as I can.
The virtualization overview raises some questions for me, especially around KVM. KVM is a hardware-assisted virtualization technology, providing access to the underlying capabilities of the processor. In this, it is much like LDOMs on T series SPARC systems. KVM will not function well on CPUs that do not include the hardware virtualization extensions. The RHEV product uses the same KVM technology for the hypervisor layer. While the resulting configuration more resembles Containers than LDOMs, the technology more closely maps to LDOMs. The use of VMware to achieve this style of virtualization is not necessary.
With Xen moving out of the maintained RHEL stream, there is no supported purely software virtualization solution for Red Hat.
Hi Matt, you bring up a good point about the many subtle points surrounding virtualization. I would still put KVM in the software-based virtualization camp though, as most of the virtualization it does happens in software. Intel and AMD CPUs provide support for virtualization but not a full hardware-based hypervisor such as LDOMs. I agree though that even software-based solutions like KVM are quite powerful and efficient because of the hardware support in the CPUs. Software like Xen and OVM also take advantage of that support as well.
Hi Peter,
Really good documents detailing the DC OSes worth comparing. Thanks for these documents.
I have a question with reference to some of the points mentioned in the first part under Scalability and Performance. You have mentioned that RHEL scales to only 32 Cores and 16GB of memory on the x86 systems, does this mean that one cannot deploy RHEL 5 or 6 on the latest Intel based servers scaling to 64 cores with 512GB Memory as once instance without Virtualization? I ask this question as these limitations are definitely stated on the RHEL website as well but do not mention these limits for their Virtualization using KVM.
Thanks once again and look forward to more documents from your end.
Regards,
Sachin Bhat
Hi Sachin, Yes, I believe those were the limits for RHEL 5. However RHEL6 states much higher limits when running in 64-bit mode. The spec sheet is here if you want to see all the details: http://www.redhat.com/f/pdf/rhel/RHEL6_datasheet.pdf
I recently had a look into an new Redbook by IBM (IBM Data Center Networking: Planning for virtualization and cloud computing).
It identified the following types and subtypes of hypervisors (page 45 ff.) and I tend to agree, that this is far better than trying to seperate “hardware” from “software” virtualization:
Type 1: Virtualization code that runs directly on the system hardware that creates fully emulated instances of the hardware on which it is executed. Also known as “full”, “native” or “bare metal”.
Type 2: Virtualization code that runs as an application within a traditional operating system environment that creates fully emulated instances of the hardware made available to it by the traditional operating system on which it is executed. These are also known as “hosted” hypervisors.
Containers: Virtualization code that runs as an application within a traditional operating system that creates encapsulated, isolated virtual instances that are pointers to the underlying host operating system on which it is executed. This is alsow known as “operating system virtualization”.
Type 1 or bare metal hypervisors are the most common in the market today, and they can be further classified into three main sub-types:
- Stand-alone (e. g. VMWare ESX and vSphere)
- Hybrid (e. g. Hypver-V or XenServer)
- Mixed (e. g. Kernel Virtual Machine)
Regards,
Töns