User guide

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both the speed in which the desktops are available to the customer and overall customer experience. A ―virus
scan storm‖ is similar to a boot storm in I/O but might last longer and can significantly affect customer experience.
Due to these factors, it is important to make sure that the storage is architected in such a way as to eliminate or
decrease the effect of these events.
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Aggregate sizing. An aggregate is NetApp‘s virtualization layer, which abstracts physical disks from logical
datasets, which are referred to as flexible volumes. Aggregates are the means by which the total IOPS
available to all of the physical disks are pooled as a resource. This design is well suited to meet the needs
of an unpredictable and mixed workload. NetApp recommends that whenever possible a small aggregate
should be used as the root aggregate. This root aggregate stores the files required for running and
providing GUI management tools for the storage system. The remaining storage should be placed into a
small number of large aggregates. The overall disk I/O from virtualization environments is traditionally
random by nature, so this storage design gives optimal performance because a large number of physical
spindles are available to service I/O requests. On smaller storage systems, it might not be practical to have
more than a single aggregate, due to the restricted number of disk drives on the system. In these cases, it
is acceptable to have only a single aggregate.
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Disk configuration summary. When sizing your disk solution, consider the number of desktops being served
by the storage controller/disk system and the number of IOPS per desktop. This way one can make a
calculation to arrive at the number and size of the disks needed to serve the given workload. Remember,
keep the aggregates large, spindle count high, and rotational speed fast. When one factor needs to be
adjusted, Flash Cache can help eliminate potential bottlenecks to the disk.
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Flexible Volumes. Flexible volumes contain either LUNs or virtual disk files that are accessed by Citrix
XenDesktop servers. NetApp recommends a one-to-one alignment of Citrix XenDesktop datastores to
flexible volumes. This design offers an easy means to understand the Citrix XenDesktop data layout when
viewing the storage configuration from the storage system. This mapping model also makes it easy to
implement Snapshot backups and SnapMirror replication policies at the datastore level, because NetApp
implements these storage side features at the flexible volume level.
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Flash Cache. Flash Cache enables transparent storage cache sharing and improves read performance and
in turn increases throughput and decreases latency. It provides greater system scalability by removing
IOPS limitations due to disk bottlenecks and lowers cost by providing the equivalent performance with
fewer disks. Using Flash Cache in a dense (deduplicated) volume allows all the shared blocks to be
accessed directly from the intelligent, faster Flash Cache versus disk. Flash Cache provides great benefits
in a Citrix XenDesktop environments, especially during a boot storm, login storm, or virus storm, as only
one copy of deduplicated data will need to be read from the disk (per volume). Each subsequent access of
a shared block will be read from Flash Cache and not from disk, increasing performance and decreasing
latency and overall disk utilization.
3.5 FlexPod Technical Overview
Industry trends indicate a vast data center transformation toward shared infrastructures. Enterprise customers are
moving away from silos of information and moving toward shared infrastructures to virtualized environments and
eventually to the cloud to increase agility and reduce costs.
FlexPod™ is a predesigned, base configuration that is built on the Cisco Unified Computing System™ (Cisco®
UCS), Cisco Nexus® data center switches, NetApp® FAS storage components, and a range of software partners.
FlexPod can scale up for greater performance and capacity, or it can scale out for environments that need
consistent, multiple deployments. FlexPod is a baseline configuration, but also has the flexibility to be sized and
optimized to accommodate many different use cases.