Xen is a "hypervisor" that lets a single
computer run several operating systems simultaneously, using
an idea called "virtualization." This enables companies to
use a single server more efficiently--something that could
save them money. Now "containers," a higher-level
virtualization approach that makes a single operating system
look like many, is also getting traction.
High ImpactWhat's new:
Novell and Red Hat have concrete plans to build "container"
virtualization into their Linux products
Bottom line:
The virtualization technology, which makes a single
operating system look like many, could increase the
efficiency of server use and so save companies money--but it
does have some limitations.
More stories on virtualization
Specifically, containers are likely to appear in the next
major versions of Red Hat Enterprise Linux (RHEL) and
Novell's Suse Linux Enterprise Server (SLES). The technology
could even be added before those updates, company executives
said.
Two projects are under way to bring containers to Linux:
Vserver and OpenVZ, the latter backed by a company called
SWsoft. Overall, their prospects look bright.
"I think the big advantage of a containers approach,
compared to a hypervisor, is a lot less overhead. You get
much higher performance," Gabriel Consulting Group analyst
Dan Olds said.
Containers are increasingly popular. Sun Microsystems
introduced its own container technology in 2005 with Solaris
10. And Microsoft is working on an adaptation of existing
technology.
They are not suited to all tasks. Containers require all
applications to use the same copy of the underlying
operating system, for example. Xen and the established
virtualization leader, EMC's VMware, don't have that
requirement. Nevertheless, containers are desirable.
Next on the agenda
"It's something that we want to see happen," Red Hat's chief
technology officer, Brian Stevens, said in an interview here
during the LinuxWorld Conference & Expo. Red Hat hasn't
decided whether to use OpenVZ or Vserver, he added.
Xen is the priority for RHEL 5, due to arrive at the end of
the year, but after that will come containers, Stevens said.
"I'm looking at that as a RHEL 6 thing," he said.
Novell, which wants to maintain Suse's reputation as the
first place to find advanced new features for Linux, is more
eager and is considering adding OpenVZ in Service Pack 1 of
SLES 10. "We are still evaluating if this is something we
can take into SP1," said Holger Dyroff, vice president of
Linux product management.
If containers don't arrive with SLES 10 Service Pack 1,
Novell will urge SWsoft to work with Linux programmers so
that the software can be easily added to SLES 11, Dyroff
said.
Debian Linux, a noncommercial version of the open-source
operating system, added OpenVZ to its "Sid" development
version in August.
And some work being done for Xen will help pave the way for
containers. Specifically, this will provide management tools
that let customers start, stop and otherwise control virtual
machines. The same technology can be used to control
containers, Stevens said.
"It'll be a lot easier next time. We'll be able to just plug
it in. There already will be tools to manage it," Stevens
said.
But SWsoft, the company that is sponsoring the OpenVZ and
that sells a fuller-featured commercial version called
Virtuozzo, sees things the other way around. Last week, the
company announced that its container management tools will
also be able to manage Xen virtual machines, said Chief
Executive Serguei Beloussov.
On a diet
The main reason to use containers is because they require
fewer computing resources than full-fledged virtual
machines.
For example, the many components of an operating system and
its applications must be loaded into memory only once, and
multiple containers can use the same copy. However,
containers still need unique memory for their own data
storage.
Another advantage is that some processor resources are used
more efficiently with containers, said Don Becker, Penguin
Computing's CTO and a Linux supercomputing expert. For
example, a chip's translation lookaside buffer (TLB), which
converts an operating system's memory addresses into the
physical locations that the computer actually uses to fetch
needed information, is dramatically more useful with
containers, he said.
Sun's containers, also called "zones," take only an extra
60MB of memory apiece, said John Clingan, a Sun engineer who
has seen just how many he can squeeze onto a single server.
"Zones are very lightweight," he said. "I fit 600 containers
running Apache on an 8GB four-processor box," referring to
Web server software.
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