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Virtual Machines

Overview

Research Computing offers hosted virtualized servers for groups requiring dedicated systems. Virtualization helps avoid the cost of investment in dedicated hardware where raw horsepower or highly computational usage is not a concern. This document aims to outline our offerings and the levels of support offered on the various tiers.

TIERDESCRIPTIONADMINISTERED BY
1Fully monitored, RC is responsible for service availability and proper functioning of the base VM. No sudo/root access. NFS mounts allowed.FAS RC
2RC provisions requested OS, end-user has limited privileged access (example: May have sudo to restart webserver). NFS mounts allowed.FAS RC & Customer (limited)
3RC provisions "bare metal" with requested OS, hands off to requester who has administrative control. No NFS mounts allowed, as a result. RC is responsible for proper functioning and health of the KVM infrastructure. End-user is responsible for all other maintenance including software and administration of services.Customer

Standard Offering

While we strive to be as flexible as possible, so that your group's needs can be satisfied, we do have a default base configuration. This allows us to have a full understanding and control the systems while offering the best support possible. As configurations drift away from this standard default, they require more time and effort to support when something goes wrong. Please bear that in mind when requesting a VM.

Virtual Machines are suitable for many applications and usage models, but are not suitable for use as compute nodes, database or other disk intensive services, or computational/visualization nodes. Please contact us to discuss how best to implement those services for your lab or group.

Our default offering consists of a modestly configured VM, well suited to most low-to-mid end tasks. These systems are:

  • OS: CentOS 7.x
  • Virtual CPUs (VCPU): 2
  • RAM: 2GB
  • Networking: 1x1GB static network address, public IP addresses available as requested.
  • Disk: 20GB.

We have found that for most tasks, these specs are suitable, and this smaller footprint allow us to efficiently host many VMs in a small amount of space with very little power consumption.

VCPUS and RAM can both be extended, within reason. Research Computing staff can help you determine the best RAM and VCPU ratios. But please be aware that our VM pools by design are a shared resource, as such we do need to place limits on the maximum VM size and how much in total each group can utilize at one time.

  • Max Total Allowable Size for any Single VM: 8 VCPU Cores/16GB RAM
  • Max Combined RAM and VCPU Per Group for all VMs: 16 VCPU Cores/64GB RAM

If you need a machine larger than the maximum offering or more total cores than the maximum quota, please contact us to discuss purchase of a dedicated hardware node.

VM Storage

For disk storage, our approach is to keep disk images as small as possible, for maximum flexibility and efficiency (the bigger they are, the harder they are to move around quickly as things change). Smaller disks also allow VM backups to happen in a timely manner. Obviously not all applications/use cases can be satisfied with a 20GB disk which includes the OS. When this is the case our preferred path it to expose network storage (many times Shared Lab/Group storage, or storage specifically provisioned for this service) for additional capacity (see Tier table above for exceptions).

Backups of VM disk images/configurations happen nightly, and 2 weeks of history of these is retained. That being said, it is much easier/effective to restore from backups of network shared storage(it is more granular, with the VM disk image, the entire disk would have to be restored, not simply a part/section of it), and is yet another reason we encourage small disk images with network shared storage for data.

We can be flexible

As always we are here to work with you and your needs.  Except for the quotas defined above, we will do our best to accommodate different system specs as needed (more advanced networking configuration, different OS, backup history length, special software needs, etc.)

As always, please contact us with any questions about VM hosting via the RC Portal or email rchelp@rc.fas.harvard.edu

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