At VMworld Europe in Cannes, France, storage players Pillar Data Systems and Double-Take Software Inc. took the opportunity to launch virtualization enhancements to their respective products: in Pillar's case, the Axiom midrange modular storage area network (SAN) array, and in Double-Take's, the Double-Take for VMware Infrastructure 3.0 replication software.
And while the announcements address different types of storage products, together they underscore the fact that current-day SANs leave much to be desired when used to house and protect virtual machines.
For Pillar's Rob Commins, director of product marketing, one of the most grievous problems is the difficulty in tuning SAN arrays for optimal I/O performance. That in turn prompts IT shops to overspend on larger, faster storage subsystems than they really need, "neutralizing or eclipsing the economic benefit of server virtualization," Commins said.
"The ROI isn't right because you're just moving dollars from servers to storage."
Commins explained the problem as follows: As it stands, most VMware administrators map a VMware Virtual Machine Disk (VMDK) to a SAN logical unit number (LUN) on a per-host basis. The ESX host then "round-robins the I/O to the storage, making it look random and chaotic," Commins said. "What we see is I/O coming down [from various virtual machines] all interleaved with each other, creating I/O that cannot be sorted out."
But the very nature of server virtualization is that any given ESX server houses virtual machines (VMs) running a variety of different applications, each of which benefits from its own optimal I/O configuration.
For example, a database redo log should be placed on storage configured for small, random, write-intensive I/Os, Commins said, which is achieved by placing the data on a very thin band of a hard-disk drive and by enabling as much write cache as possible. Conversely, the I/O profile of a backup-to-disk job is write-intensive and sequential, and "hates write cache," Commins said. File serving, meanwhile, "is sort of a tweener," Commins said, and likes mixed-read/writes and medium-sized I/Os.
Pillar's application profiles for VMware should help IT administrators easily optimize SAN storage for the workload running in a given virtual machine. It will also offer application profiles for Oracle VM, Oracle's Xen variant. Pillar is an Oracle spinoff. The application profiles will be a feature of Pillar's Axiom storage array, and assigned from its management GUI. Examples of application profiles include Web and file serving, database and data protection schemes. In addition, Pillar will welcome new application profiles from its customers and channel partners, and will make them available as free download when they become available, Commins said.
Virtualization administrators that adopt the Pillar application profiles will probably find themselves configuring their SAN storage differently, assigning one VMDK per LUN, or at least "a grouping of similar VMDKs," Commins said. "The unit of granularity is a LUN or [in the case of NAS], an NFS [Network File System]." Large, performance-sensitive VMware shops already do a form of that by maintaining multiple classes of SAN storage to which they can map virtual machines, but this marks the first time that smaller shops can easily map VMs to optimally configured LUNs, Commins said.
Double-Take doubles down on VM replication
Meanwhile, Double-Take Software now offers an enhanced version of its Double-Take for VMware Infrastructure 3.0 replication software, which targets VMware ESX shops that want a cost-effective way to protect virtual machines without investing in high-priced SAN-based replication software in both the primary and remote recovery site.
Avoiding the purchase of SAN replication software "reduces the protection tax associated with disaster recovery," said Bob Roudebush, Double-Take's director of solutions engineering.
Double-Take for VI3 installs on a standard Windows server, often the same server that hosts VMware VirtualCenter. From there, it integrates with VMware's APIs to take periodic snapshots of replicated VMs, and orchestrates the replication of the change logs between the primary and secondary ESX hosts.
Some of the notable new features in Double-Take 3.0 include the following:
- improved failover and restore capabilities;
- the ability to restrict bandwidth usage not only per ESX host but also per individual VM;
- block-level checksums that trace back to the initial replication. "In the past, if the replication were to fail, you would have to start the replication job over from scratch," Roudebush explained; and
- simplified management and installation, even in environments without VMware VirtualCenter. "If you're a small customer and you don't have VirtualCenter, we will provide you with our own management console," Roudebush said.
Double-Take for VI 3.0 is available immediately, and priced at about $2,495 for up to five protected virtual machines. Replication of VMs is not restricted to any particular ESX hosts. "The whole idea is to make it as easy as possible to buy and protect your virtual environment," Roudebush said.
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