A blog about server hosting

Now virtualisation has reached maturity, virtual servers are a real alternative to dedicated servers.  However, they’re not ideal for all situations.

From our point-of-view we’re seeing virtual servers as a great alternative to our entry-level dedicated servers, and a great deal faster than older dedicated servers running on deprecated hardware.

That said, they’re not perfect for everything, and there are many applications where only dedicated will suffice.

Here are some of the aspects of virtual servers to consider:

• CPU is burstable. With a virtual server, you’re allocated a smaller slice of a higher-end CPU than you’d have in a low-end server.  In our case, we’re using Xeon L5420s  and L5520 processors in our virtual server nodes.  These are faster by quite a stretch than the CPUs found in our entry-level servers.  Obviously you don’t have all of this power at your disposal, but  when there are idle cycles, you are free to grab them.  And given that the average CPU usage on our VM nodes is < 10% on average, the end result can be much faster than that 3-year-old chip in that cheap dedicated.
• I/O is burstable. Slow disk IO is usually the most criticised short-coming of VPS, but it only happens on overcrowded boxes.  In our case, you’re connected to a SAS or SATA SAN (dependant on which storage you pay for) which is running RAID50, connected by a 2Gbps iSCSI connection to the host node.  The End result? Much faster disk I/O with our SAS option, when compared to the disks you find in a low-end dedicated server.
• Better Resiliency. Compared to a cheap dedicated, you’re getting a slice of a machine which has redundant power supplies, fed from two UPSs, dual uplinks to both frontend and storage networks, and RAID50 storage, with hot-spare disks on our high-availability SAN (with off-site replication too).
• Better for the environment. Because hardware is better used, less electricity is consumed per virtual server.

Good candidates for virtualisation:

• Servers which have low CPU and/or memory usage, but with occasional peaks.
• Servers which can be scaled horizontally, for example web servers behind a load-balancer.
• Single-service servers, i.e. those running a single website or email.
• Servers which need to have CPU and/or memory upgraded for short periods, without excessive downtime associated with hardware upgrades.
• Staging environments needing a fraction of the resources of the live environment they mirror.
• DR environments which usually need very little resource but need to be scaled upwards quickly.

Bad candidates for virtualisation:

• Servers needing access to multiple CPUs or masses of memory (i.e. the largest VM we offer as standard has 4GB of RAM and 2 CPU cores).
• Servers needing huge amounts of storage space.  This is due to the high cost of SAN-based storage.  Once you get above a certain threshold, it becomes cheaper to use a dedicated server fitted with a RAID5 SAS disk array.

Mix-and-match

The great thing about the way we can provision servers means that your virtual and dedicated servers can sit on your own private network (VLAN), and communicate with each other freely.  This means that you have the flexibility to use the right mix of servers based on the individual requirements of each element of your hosting platform.

Our technical team, in conjunction with our account managers, can help to advise on what’s right for any given situation.