Frequently Asked Questions

Why does Delphix recommend 8 vCPUs and 128GB of memory per 8 vCPUs?

8 vCPUs are not only a standard licensing block, they are key to meeting our 10Gbps single-engine throughput potential and help to sustain low latency for vDBs.

As with CPU, cache memory is required to drive peak loads on the Delphix Engine. More memory allows for more blocks to be read from cache rather than going to less performant disks. Delphix stores cached data in a compressed format and only keeps a single copy of unique blocks in memory. These features give read performance across multiple VDBs provisioned from a single source dramatic improvements in speed,  scalability and memory utilization.

Why does Delphix request reservations for CPU and memory?

Delphix performance can be greatly impacted there is contention over CPU or RAM. Reservations allow the engine to explicitly control those resources and avoids the possibility of contention with other VMs, even when resources are overcommitted.

Why does Delphix request Hyper-Threading (HT) be disabled?

Hyper-Threading can have a positive impact on many, but not all applications. Delphix has a different execution profile that does not benefit from Hyper-Threading. Factors such as significant memory bandwidth requirements and a high level of parallelism which requires a high number of shared locks mean that HT and Delphix do not generally work well together.

Why does Delphix request 4 controllers, and why must the storage be identical between them?

To provide optimal storage performance, you must spread data equally over the maximum (4) virtual SCSI controllers. To provide consistent performance between each of the four controllers, you need to ensure storage is identical between them.

Why must virtual disks (VMDKs) be thick provisioned and eager-zeroed?

Thick provisioning and eager zero ensure performance is top-notch from the start with no hiccups from expanding virtual resources.

Why is 20% free space required?

While the ZFS file system has a lot of features leveraged by Delphix, it loses efficiency as space decreases. 20% is the minimum that must be available for best performance.

Why does Delphix request you reserve CPU and RAM for Hypervisor overhead?

Based on VMWare’s resource management guide and our own experiences with high IO throughput. Note there is no specific mechanism to assign resources to the hypervisor, the only way to preserve overhead is by not allocating resources to guests.

Why does Delphix generally want VMWare HA enabled, but DRS disabled?

VMware HA (High Availability) addresses outages that occur when a physical host goes down or is completely offline, by migrating the guest(s) to another physical host and restarting them. There is no real downside, it simply brings unavailable servers back online.

VMware DRS (Distributed Resource Scheduler) is for load balancing host resources in a cluster. Because of high IO and best practices configuration for optimal performance, our engine is typically not a good candidate for relocation.

Why does Delphix request you set power management to High Performance Mode?

This will ensure power management will never impact performance by entering into a lower power state (also known as c-state).