I'm a firm believer in the necessity of disk defragmentation. While some people maintain that solutions providing "always on" defragmentation are unnecessary in modern OSs with large amounts of RAM and intelligent caching of commonly accessed files, I've found that these programs turn a fast computer into one that's snappy. Although this isn't a night-and-day difference, it's an improvement that some users are prepared to pay for. Despite this, I've had a long-standing love-hate relationship with Diskeeper software. Only with the release of Diskeeper 2011 and its inclusion of the Efficient Mode have I been truly satisfied that the program isn't constantly chugging away at my disks aiming to maintain a perfectly defragmented state at all times, which is indeed unnecessary.
Many servers now utilize virtualization of one kind or another. File caching isn't optimized to work with virtualized workloads and it's unlikely that there's ever going to be enough RAM, so raw disk performance comes back into the spotlight. Based on the same defragmentation engines as Diskeeper 2011, V-locity runs on Hyper-V host servers, providing local disk and SAN defragmentation. During the defrag process, it monitors agents deployed on the guest virtual machines (VMs) to ensure there's no contention for disk resources. V-locity requires a separate Windows VM (or physical device) to run the host software in VMware virtual infrastructures.
V-locity supports Windows XP SP2 or later and Windows Server 2003 or later guest OSs on Hyper-V and VMware ESX/ESXi 4.0 or later hosts. VM guests are also supported in Citrix XenServer.
My test system consisted of Hyper-V running on Windows Server 2008 R2 with a collection of Windows Server guest VMs. I found that installing the host software is straightforward and includes a warning that Windows Firewall settings might need to be modified if Diskeeper Administrator will be used to manage V-locity.
When installing the V-locity guest software on a VM, you have two additional options to configure:Enable Automatic Defragmentation on all volumes on this computer and Enable Automatic Space Reclamation on all volumes on this computer. Both are enabled by default.
Understanding the Technologies
V-locity uses a variety of technologies to defrag physical and virtual disks. IntelliWrite replaces NTFS write logic to minimize defragmentation as files are written to disk. To avoid interfering with SAN optimization, Instant Defrag cleans up any fragments that occur while the write is still in process. InvisiTasking ensures that any defrag activity happens using idle processor cycles, while CogniSAN and V-Aware monitor VMs on local disks and SANs to ensure that there's no contention for resources as guest VMs defrag their local disks.
V-locity is able to detect different types of Virtual Hard Disks (VHDs), optimizing defrag routines to minimize unnecessary disk growth. Space reclamation works in conjunction with live migration tools to compact VHDs during the migration process. V-locity automatically zeros out unused data blocks on VHDs so that Automatic Space Reclamation can run while a disk is online. VHDs can also be compacted manually if they're dynamic (or thin in VMware terminology) and offline. Finally, I-FAAST organizes files on the disk to provide the fastest access to frequently used files.
Once installed, you probably won't touch the management interface very often, apart from the occasional need to compact VHDs. One disadvantage is that you must log on to each guest VM to perform management tasks, as there's no centralized view from the host server. Finding your way around the management console is intuitive, with all the discovered disks listed at the top of the window and statistics on current operations and performance of the defragmentation engine shown below. On the host server, the management interface lists all guest VMs on which V-locity has been installed (see Figure 1), which is a comforting indication that the software is able to detect disk usage across all the virtual systems.
V-locity reported a 34 percent I/O improvement after installation on my Hyper-V host. You can generate reports for individual disks by clicking Analyze. This report contains detailed information about a disk's current state and performance.
A Low-Cost Performance Boost
The best thing about V-locity is the price. It's licensed per CPU on the host with an unlimited number of VMs. Despite the software's management shortcomings, at this price it's a no-brainer. Diskeeper Administrator can be licensed at an additional cost if you need to manage a large number of V-locity hosts. Smaller shops can probably survive without the extra management functionality because V-locity largely does its stuff without the need for constant monitoring.