Double-Take Software Inc. has announced its replication software
will now replicate virtual machines at the ESX level, a move users
said could be more cost effective and shrink restore times for
virtual machines.
Previously, an instance of Double-Take's software had to be run
inside each guest server operating system, which quickly grew
cumbersome for users on both the licensing and management front.
Last April, Double-Take announced an update to its licensing
structure that would allow users to buy licenses in a "pack" that
would support five virtual machines at one price.
Now, the software itself has been updated to replicate the entire
physical machine and all of its guest operating systems through
integration at the kernel level with VMware Inc.'s ESX server. This
update, which Double-Take is calling Double-Take for Virtual
Infrastructures, will dampen the granularity of the software that
replicates file-level changes. But users said it's a tradeoff
they'll gladly make for cheaper licensing and faster restores.
"Before they announced the ability to replicate virtual
servers," said Praneeth Machettira, Technical Director in the
Office of Technology Management for Sawyer Business School at
Boston's Suffolk University. "there really wasn't anything specific
in the product that was different for virtual machines."
Under the previous version, each guest OS had to be replicated
separately, Machettira said. "Even with the licensing packs, you
were still talking about building another ESX server, adding the
servers individually, and doing that for every guest OS you wanted
to replicate," Machettira said.
Licensing will also be key, according to Machettira. According
to Double-Take, the licensing for the ESX-level replication is
$2,495 per 10 virtual machines without restriction on how they are
distributed over physical machines.
"It seems like a good price," Machettira said, "especially
knowing that Double-Take is fairly easy to manage."
Still, though the new capability looks good on paper, Machettira
added that he would be cautious in deploying the new version of the
software.
"I probably won't implement this right away," he said, "I don't
know how strong Double-Take's partnership with VMware is, and we're
still talking about integrating with the ESX kernel at a
proprietary layer—I'm going to let it sit for a while."
Feeding into the iSCSI-VMware boom
Double-Take VAR Michael Paynter, managing partner for Tier-3
Technologies in Louisville, Ky., said he thinks the update to
Double-Take's software will further widen the appeal of VMware in
the midmarket, similar to the popularity brought on by recent
interoperability with iSCSI SANs. (See
ISCSI brings VMware to a new audience,
Feb. 12).
"There are a lot of people in the midtier with 'paper' DR
plans," Paynter said. "Some of them have 40 or 50 machines, and
trying to do all of that using Double-Take's former licensing model
was still cost prohibitive."
Meanwhile, Paynter said, as a reseller and system integrator of
WAN optimization products as well, he would like to see Double-Take
add the ability to send just changes over the wire. "Even if you're
doing optimization, sending a full virtual machine across the WAN
is still a lot of data on the network."
Currently, according to Bob Roudebush, director of solutions
engineering for Double-Take, the product currently sends delta
changes on each scheduled replication, with a maximum replication
frequency of 15 minutes or after every 32 MB of change. "Byte
level, continuous replication in ESX hypervisor requires
enhancements to ESX, and we are part of the VMware community source
effort to work on that," Roudebush told SearchStorage.com in an
email.