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Latest VMware rev tackles storage shortcomings

Large VMWare shops have high expectations for the storage capabilities of the server virtualization platform. Tom Becchetti, senior capacity planner at a national financial services firm, has 37 VMware ESX Server 2.5.3 hosts running 140 virtual machines and is "kicking the tires" on VMware Infrastructure 3 (VI3). As it stands, "the underlying ESX file system is a good foundation," he says. But, "ultimately, what you want is a full foundation like a [Symantec] Veritas [file system and volume manager]," he notes, with the ability to do things like dynamically add and resize volumes.

VI3, which was announced this summer, takes some steps in that direction, thanks to several enhancements to Virtual Machine File System (VMFS), ESX Server's underlying clustered file system. VMFS now delivers better I/O performance across a range of file sizes.

Virtual Machine Disk Format (VMDK) files tend to be large--as big as 2TB--and are thus characterized by large block I/O patterns, explains Patrick Lin, VMware's technical director of product management. There are also smaller files associated with a virtual machine (VM) that describe its configuration and state, he says. Therefore, VMFS has been equipped with adaptive block-sizing capabilities to better meet the I/O needs of the various files in its jurisdiction.

VMFS volumes are now more flexible and can be shared among 32 ESX hosts, says Lin, while distributed journaling capabilities allow for the quick recovery of a VM in the case of a server failure.

But the real showstopper enhancement, according to Lin, is the way VI3 now supports the dynamic expansion of virtual disks, the volumes that contain the VM. "Before, you would have to power down the VM," says Lin. At VMworld last fall, the announcement of this feature "got a round of applause from the audience," he notes.

Enhancements to VMFS affect several other VI3 capabilities. ESX Servers running VMFS can share a single pool of network storage, as well as the VMDK files that comprise a virtual machine. VMFS is instrumental in allowing VMware VMotion to re-home a VM to a new machine if VMware Distributed Resource Scheduler has determined that it's running poorly or if VMware High Availability has detected a failure. "VMFS is a prerequisite for a lot of the more interesting things we can do with virtualization," says VMware's Lin.

VI3 also tackles the issue of backing up a VM. In the past, there were two methods for backing up VMs: You could run the backup agent from the ESX Server console and back up the VMs as single, large VMDK files. This method works fine, but it doesn't give you any view into the contents of the VMDK, notably, the files within it. The other alternative is to run the backup from within the VMs themselves. This approach provides a view into a VM's files but, says Lin, can be a real drain on ESX Server resources.

"With a traditional machine, you can usually assume you have extra capacity and processing cycles to achieve your backup window," says Lin. "When you start consolidating applications on ESX, the idea of extra resources doing nothing that can be applied to backup becomes problematic."

VI3 addresses these shortcomings with Consolidated Backup, which supplies a driver that takes snapshots of the virtual disks that can then be mounted onto a separate non-ESX Server. From there, they can be backed up as usual by the regular backup server. "Think of it as offloaded file-level backup," says Lin.

Users hope Consolidated Backup can save them money. Tony Bergen, manager of server technologies at The North West Company Inc., a retail distributor in Winnipeg, Manitoba, is a VMware ESX 3 user and is considering Consolidated Backup.

A Symantec Veritas NetBackup shop, The North West Company currently backs up only guest VMs; but with Consolidated Backup, "we won't need an agent license for each VM," says Bergen. The decision to go with Consolidated Backup will depend on how much Symantec charges for this support. "I bet Symantec/Veritas will price the agent pretty good," he says.

Finally, VI3 adds native iSCSI support, expanding the range of shared storage platforms that can be used in a virtual environment. Older versions of VMware supported only Fibre Channel (FC) natively. If you wanted to run iSCSI, it was necessary to load an iSCSI driver onto each VM.

ESX shops have an abnormally high SAN attach rate--approximately 70%, says John Chevalier, director of product marketing at FC host bus adapter maker Emulex vs. only approximately 20% of servers overall. The possibility of attaching to a SAN using commodity Ethernet infrastructure may push the SAN attach rate even higher.

--Alex Barrett

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