10 tips for managing storage for virtual servers and virtual desktops


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#6 Don't forget to monitor. People usually pay attention to storage statistics when problems occur, but data storage requires attention on a continuous basis. If you don't monitor your storage performance on an ongoing basis you might not know of potential problems or bottlenecks, or be able to spot trends or patterns that may allow you to act proactively. It's particularly important when using network-based iSCSI and NFS storage because network health can impact storage performance. Storage performance should therefore be monitored at both the virtualization layer and storage layer, as a problem may be visible from one viewpoint but not the other. Monitoring a virtual environment is not as simple as monitoring a physical environment. Products designed for virtual environments that monitor end-user or application experiences can help pinpoint exactly which resource or component may be causing a bottleneck.

#7 Watch out for storage threats that can grow. Virtual machine snapshots and thin provisioned virtual disks represent a double threat as they have the potential to consume all of the disk space on your VM data stores, which can potentially crash or shut down your running VMs. If you plan to overcommit your storage using thin disks, you need to closely monitor their growth. Don't rely completely on thin disks to address disk space woes; try rightsizing VM disks when you create them and don't give them a lot more disk than they need.


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are an even bigger threat, as VMs can have multiple snapshots with their combined space much larger than the original virtual disk file size. While VM snapshots can be a handy tool, you should never use them in lieu of traditional backups. Not only do snapshots take up additional space, they can reduce data storage performance. That's especially true when you delete a snapshot and the delta disks are written back to the original disks causing intense disk I/O while the operation is occurring. For very large snapshots, try scheduling their deletion during off hours when the extra I/O will have less of an impact.

Don't rely on manual methods to monitor thin provisioning and snapshots. For thin disks, set alarms for specific overcommitment percentages so you'll know when your data stores are becoming overcommitted. For snapshots, use alarms to look for snapshots that grow beyond a certain size. You should also use alarms to monitor data store free space to alert you when space is low. Be sure to set your alarms high enough, as thin disks and snapshots can sometimes grow very quickly and there might not be much time to respond. Don't rely completely on alarms for snapshots; use regular reporting tools to identify snapshots so they don't run longer than needed.

#8 Integrate server virtualization with storage management. More and more storage vendors are integrating server virtualization and storage so they can be managed and monitored using a single console. Examples include plug-ins developed for VMware vCenter Server from NetApp (Virtual Storage Console) and EMC (Virtual Storage Integrator) that allow storage arrays to be managed from vCenter Server. This type of integration allows for much simpler management of the storage devices used by virtual hosts because monitoring, provisioning, replication and other storage operations can be done directly from vCenter Server.

Storage vendors are also leveraging virtualization APIs to provide very tight integration between the storage layer and the virtualization layer. Using the VMware vStorage APIs, storage tasks traditionally handled by the virtual host (e.g., block zeroing, Storage VMotion) can be offloaded to the storage array, thereby freeing up host server resources. The APIs also provide more intelligent multipathing to achieve better I/O throughput and failover, and offer replication integration for products like VMware's vCenter Site Recovery Manager.

#9 Traditional methods might not cut it. Moving from a physical to a virtual environment also requires a change in thinking. Things like backups, server provisioning, monitoring and management are all very different once servers are virtualized. Applications written specifically to monitor and manage physical environments typically aren't effective in virtual environments because they're not aware of the virtualization layer between the server hardware and the guest operating system.

With backups, for example, it's not efficient to back up servers through the OS layer on virtual hosts. Instead, most virtualization-aware backup apps go directly to the virtualization layer, which is quicker and more efficient. Performance monitoring is another example: If you monitor using OS tools that aren't aware of the virtualization layer, the results will often be inaccurate as the OS tools don't have direct access to the underlying host hardware.

#10 Prioritize storage traffic. Hosts with many virtual machines running on them can be like the Wild West with all of the VMs fighting for the host's limited resources. You can end up with less-critical VMs impacting the resources of critical virtual machines and the resources available for host operations. To prevent this kind of contention, consider using storage I/O controls that can provide a Quality of Service (QoS) level for certain critical host functions and VMs. VMware's vSphere 4.1 introduced a new feature called Storage I/O Control (SIOC) that works by measuring storage latency; when a set congestion threshold is reached for at least four seconds, it enforces configurable I/O shares on VMs to ensure the highest-priority virtual machines get the I/O resources they need. SIOC should help restore some order on busy hosts and allow VMs to coexist peacefully by making it less likely that a few rogue VMs will drag down your critical virtual machines.

BIO: Eric Siebert is an IT industry veteran with more than 25 years of experience who now focuses on server administration and virtualization. He's the author of VMware VI3 Implementation and Administration (Prentice Hall, 2009) and Maximum vSphere (Prentice Hall, 2010).

This was first published in October 2010

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