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BP1018 Sizing and Best Practices for Citrix XenDesktop with Dell EqualLogic Storage 18
As explained in section 3.3, the key components of a VDI hosted using PVS are vDisk, write cache, and
the CIFS share. The vDisk and write cache components are the most critical components and have a
huge impact on the underlying storage. CIFS share is a recommended way to separate user data from
system data because it helps simplify the user data management.
We analyzed the I/O activity on vDisk, write cache, and CIFS share for all of the above test scenarios.
The I/O activity on vDisk and CIFS share was similar for all of the above test scenarios and they are
discussed in detail in sections 5.2 and 5.3. In later sections only write cache I/O behavior will be
discussed because the vDisk and user CIFS share I/O behavior were similar across all tests.
5.2 vDisk I/O Characteristics
vDisk is the most critical component because the master OS disk image is stored on this volume. This
master disk image is streamed to all virtual desktops over the network (designed as VDI network in our
test) by the provisioning servers. There is a significant amount of read I/O activity on this volume
specifically when the virtual desktops are being booted.
In our tests, we used two PVS servers which were virtualized. Each of them was allocated with 16 GB
RAM and as a result we had 32 GB of cumulative RAM available on the PVS servers. Because our vDisk
was 25 GB, most of the vDisk contents were cached and PVS streamed the data blocks directly from
the server cache resulting in very low IOPS on the underlying storage. As a result, we observed low
read IOPS on the storage array after initial login during steady state. A single volume named “vDisk-vol”
was used to host the master OS disk image. This volume was made read-only and accessed by two
provisioning servers using Windows guest iSCSI initiators.
The SAN HQ chart below shows the I/O characteristics observed on the vDisk volume during login
storm and steady state.