Virtual Network Servers

What is a Server? 1. A software application that provides a specific one or more services to other computers  Example: Apache is a web server application  A computer can run multiple services 1. A computer that provides services to other computers  Example: I'll go and reboot the domain server

Why is a Server Different from a Personal Computer?  Speed. A server is expected to provide services to many client computers at once  Large storage capacity. If a server is to act as a central storage repository  Reliability. People in the organization may be unable to work if the server is down  Security. Data is centrally stored and must be protected

Why is a Server Different from a Personal Computer?  A server must be less vulnerable than other units.  Needs to be better quality (higher stability) than the cheap components that often are put in a cheap PC.  Down time for a server is much more expensive than down time for an ordinary PC.  And we need to be able to replace components while the machine is running

Why is a Server Different from a Personal Computer? Increased CPU power Increased I/O Therefore disks are heavily used  Need disk technology with better bandwidth  SCSI, iSCSI Components must be more robust Redundant components: everything  CPUs, RAM, fans, power supplies, NICs, disk

Why is a Server Different from a Personal Computer?  Servers usually have many users  Require high efficiency  Achieved by several factors: memory (RAM) processor (CPU) bandwidth: between components, to the network  Must support several processors and increased memory

Network Bandwidth  Bandwidth, CPU and RAM are the bottlenecks  Multiple users across a LAN. Need to get data to/from them quickly  Expect 1Gbps NIC cards. 10Gbps coming  Need a LAN design to support this  Can bond multiple 1Gbps NICs to get even more bandwidth  Again, need LAN support to do this

Internal Bandwidth  Bandwidth between components on the motherboard: CPU, RAM, peripheral sockets (i.e. NICs)  Currently PCIe 3 vs. QPI  Around 20 Gbps to 40 Gbps internally

CPUs  Multiple CPUs in each server (e.g. 32)  Multiple cores per CPU (run multiple services)  Examples: quad-core and six-core Xeon CPUs running at up to 3.5 GHz

Why is a Server Different from a Personal Computer?  24 / 7 operation therefore cooling must be effective  Choose a system case that provides good air flow  Install extra fans in the server room  CRAC: computer room air conditioning  System case should allow for server expansion

Types of Servers  File Server  Print Server  Server  Web Server  Intranet Server  Database Server  Application Server

N-Tier Server Architecture  2-tier architecture  3-tier architecture  N-tier architecture  Servers at each tier  May be on same physical server

Types of Servers  File Server  Print Server  Server  Web Server  Intranet Server  Database Server  CPU/Processing Server

Form Factor  Physical host servers live in server rooms  Rack-Mounted  Rack Unit = height  1RU = 4.5cm  Blade: multiple servers

Server Operating System  Stability  Reliability  Security  Ability to offer services to multiple client machines simultaneously

Client Server Compatibility Even if the majority of desktop computers in your organization are running Windows operating systems, the file servers can run:  Windows Server  Any Linux server operating system,  Mac OS X Server operating system (only on Apple Macintosh hardware, normally only be run in an organization which uses Apple Macintosh desktop computers.)

Data Storage Stable, reliable, secure, expandability Need extremely high bandwidth Ability to replace physical disks without stopping the server running Ability to quickly move storage space between servers as required In general, disks are now separated from the servers Connected to servers over a LAN  NAS, SAN

RAID - Redundant Array of inexpensive (or Independent) Disks  Works by copying the contents of the disks in an array to one or more others in the array.  When one disk fails and is replaced, the contents of the failed disk can be rebuilt onto the new disk from the content stored on the other disks.  The capacity of a RAID array is always less than the sum of the capacities of the disks that make up the array

RAID Levels  RAID 1: mirrors the contents of one disk onto another  RAID 5: the most common RAID level, uses three or more disks in an array, and distributes and copies the data across the disks in such a way that no data is lost if a single disk fails.  RAID 6: this is similar to RAID 5, but can tolerate up to two disks failing without any data being lost.

Server Storage External Hard Drives - Many servers use storage disks that are physically located outside the server case. Devices that provide external storage include:  Direct Attached Storage DAS: contains one or more hard drives, connected to the server.  Network Attached Storage (NAS): a device containing one more hard drives, connected to the  same LAN as the server. The server may have exclusive  use of the NAS, or the NAS may be used by  one or more other servers or client computers.

Server Storage Internal Hard Drives - hard drives fitted inside the server. Servers may sometimes house six or more hard drives, giving a storage capacity of between 2 and 6 TB without RAID.

Server Storage Storage Area Network (SAN): a complex system that connects an array of disks or other storage devices to a server over the network Completely separate network wiring than the network for the users. Need to ensure high bandwidth and low latency

Storage Area Network

And Back to Virtualisation What does this all mean for virtualisation? Server now runs multiple virtual servers  Needs MORE CPU, RAM, bandwidth  Must be even more reliable, secure, expandable Using software configuration, can more resources between different virtual servers

Example A SAN has 20TB of RAID-5 storage 3 physical servers that can run multiple virtual servers: say, 25 virtual servers. Each box has 8 CPUs and 64GB RAM The 20TB can be divided across all four physical machines because it is not tied to one machine Each virtual server can be allocated some virtual disk space from the 20TB pool

Example

Migrating Virtual Machines Because VM data storage is not tied to specific hardware, we can migrate VMs from one physical server to another Even while a VM is running (copy contents of RAM as well) Why: maintenance, disaster recovery, load balancing

Example SAN has 20TB of RAID-5 storage Four physical servers that can run multiple virtual servers: say, 30 virtual servers The 20TB can be divided across all four physical machines because it is not tied to one machine Each virtual server can be allocated some virtual disk space from the 20TB pool