Understanding DS series temporary disk size

Q. Why do DS series VMs have less temporary storage space than a normal D series VM?

A. In addition to higher IOPS, a differentiator between Azure Standard Storage and Azure Premium Storage is that while a VHD created in standard storage may have a 500 IOPS maximum. There is no guarantee you will receive 500 IOPS and the actual IOPS will depend on a number of factors but could be lower. A VHD created on Premium Storage is assured that the IOPS associated with the disk type created gives predictable performance. To achieve this predictable performance, in addition to the storage fabric changes and ensuring bandwidth between the compute hosts and the storage, there is also a larger amount of SSD cache (and RAM making up a Blobcache on the host) allocated for each VM to help with the performance. It is for this reason DS-series VMs have a smaller temporary drive than their D-series counterparts. The difference is the size that is allocated to the caching. I discuss this in more detail in FAQ Q. How do I use Premium Storage with a VM?.