Thin provisioning for virtual disks is the most eagerly anticipated storage feature in VMware Inc.'s VMware vSphere 4, according to a sampling of beta testers.
"One of the things we've been very clear about in deploying virtual servers is that storage is something we have continued to stay focused on," said Brad Blake, director of IT at Boston Medical Center, following the New England VMware User Group (VMUG) spring meeting in Newport, R.I., last week. The hospital has 500 TB on several EMC Corp. Clariion CX3 Model 40 arrays, 200 TB of which stores virtual machine data.
Many storage arrays offer thin provisioning that would allow capacity to be overallocated before being presented to the virtual server. However, before this VMware release, the virtual server itself would still demand full allocation for virtual disks and leave space unused.
"One of the biggest challenges we were dealing with, even with the most current version [VMware Virtual Infrastructure 3.5] was allocating so much storage for all the different [virtual server] instances," said Nasser Mirzai, senior director of IT at San Mateo, Calif.-based TradeBeam Inc. and a vSphere 4 beta tester.
Out of 10 TB of storage on TradeBeam's Hewlett-Packard (HP) Co./LeftHand Networks Inc. iSCSI storage-area network (SAN) set aside for virtual servers, about 8.5 TB were allocated, Mirzai said. "But we were really using about four-and-a-half to five terabytes," he added.
Attendees at last year's VMworld user conference talked about aligning virtual server and disk array-based thin provisioning, but array vendors lack that kind of visibility into VMware's APIs. Mirzai said he uses LeftHand's thin provisioning for workloads that remain on physical servers, and would like to see VMware and storage vendors integrate the process.
"Collapsing physical and virtual [provisioning] into one process, that's a match made in heaven," he said. "The biggest challenge there is collaboration between all the different storage systems and VMware – it's not very straightforward."
Using thin provisioning within virtual disks allows administrators to be selective about which systems they use the feature with. "For me, it's file services, CIFS and NFS," said VMUG attendee Ken Horn, a systems admin for an educational institution in Rhode Island that he declined to identify. "Those tend to be allocated but not actually used." As far as integration with storage arrays, "it's more important to save the space than for the array to see it from the back end," he said.
Not all VMware customers are clamoring for thin provisioning support, though. Some are cautious about thin provisioning in general.
"The downfall of any thin provisioning is that you have to be aware of how much you've committed, and at some level, that's one more thing to manage," said Ryan Makamson, systems engineer at Washington State University School of Electrical Engineering and Computer Science and a vSphere beta tester.
Makamson finds the ability to dynamically expand logical unit numbers (LUNs) more intriguing than thin provisioning. "It makes a manual process that required a machine shutdown more flexible," he said.
Fast path for storage and multipathing integration
Makamson said he looks forward most to the new paravirtualized SCSI driver that will become available in VMware vSphere. Paravirtualization makes the SCSI drivers aware that they're virtual systems communicating with the ESX layer within a box. That means the SCSI driver doesn't act as if it has to go out to an external storage switch, and it can create a fast path for storage traffic.
Boston Medical Center's Blake said the ability to integrate vSphere with EMC's PowerPath multipathing software in the new release will relieve his department of a headache when virtual machines are taken down for maintenance. Using VMware's internal multipathing, virtual servers will control the mapping of LUNs to the back-end storage system. "This will allow us to do management and maintenance reboots without the system thinking the reboot is actually a failure, and potentially spilling into another system's or application's disk space," Blake said.
Storage VMotion and the vCenter GUI
VMware Storage VMotion's integration into the vCenter GUI is also welcome news for administrators. Many had downloaded third-party plug-ins that provided a kind of band-aid integration, but they weren't officially supported and could be awkward to work with. "It saves you having to re-install the plug-in occasionally when you make an update to vCenter," said VMUG attendee Horn.
However, many of the administrators said the vCenter GUI leaves something to be desired. Horn said he'd like a single pane of glass to manage virtual servers across multiple remote locations, which has been tricky because of latency between sites. Washington State University's Makamson said he's hoping VMware launches a much-discussed Linux client for vCenter, although he hasn't seen it so far in the beta release.
The GUI can also be counterintuitive, TradeBeam's Mirzai noted. "Once you get used to it, it's a clean interface. But if you're troubleshooting trying to see why an error message is popping up, you have to do some maneuvering to get to the right logs," he said.