Data Tiering for Virtual Machines

* This feature may not apply for Single Node Systems.

This feature lets systems running SC//HyperCore™ HyperVisor on Tiered nodes (nodes with SSD disks) prioritize which data goes on SSD. HEAT is the intelligent placement and management of data on the SSD and HDD tiers in SC//HyperCore nodes. It includes:

  • SSD priority allocation that you set for each VM virtual disk, with a slide bar in the SC//HyperCore web interface.
  • Intelligent data block priority, based on block I/O heat mapping that uses I/O information from each virtual disk.
  • A system with Tiered nodes (SSD and HDD).
  • The Admin role, or the VM Create & Edit role (the VM Modify permission).

If you clone a VM virtual disk on a tiering system, the disk is mounted with a default priority setting of 4. Adjust this setting if needed before you use the disk.

Key considerations: - 10 GbE network capabilities are recommended for Tiered nodes. - By design, leave VMs at the default priority setting of 4 unless there is a specific performance need.

Customize HEAT Priority Level

Make HEAT priority changes slowly and with caution. Changing HEAT priority affects ALL VM virtual disks on the system. Each increase in flash priority access gives the VM virtual disk roughly TWICE as much flash capacity, which leaves less flash capacity for other VM virtual disks. A change to HEAT priority triggers a large redistribution of data between the spinning disk and flash disk tiers. This may reduce performance for the duration of the operation.

Scale Computing recommends moving the slider of one VM virtual disk one level up or down once every 24 hours. Change the flash priority level of only one virtual disk in any 24-hour window. Wait 24 hours for the data to be redistributed, then check performance. Repeat as needed, using the same “one level every 24 hours” rule of thumb.

Each step up from 1 through 10 on the Flash Priority slide bar doubles the virtual disk’s priority for the SSD tier. Special cases:

  • 0 — turns off all SSD access for the VM virtual disk.
  • 11 — multiplies the priority by 10.

Follow these steps:

  1. Open the Devices screen on the VM card.
  2. Click the Edit button next to the virtual disk you want to adjust. A dialog box appears, showing Allocated (current physically consumed capacity) and Capacity (total possible allowed data consumption).
  3. Use the Flash Priority slide bar to set the SSD access you want.
  4. Click Update to confirm the change. The new HEAT priority setting takes effect immediately.

If you have performance problems or questions about your VM virtual disk heat maps, contact Scale Computing Support so they can review your SC//HyperCore environment in detail.