Introduction of Server

a server is a computer program or a device that provides functionality for other programs or devices, called "clients". This architecture is called the client–server model, and a single overall computation is distributed across multiple processes or devices. Servers can provide various functionalities, often called "services", such as sharing data or resources among multiple clients, or performing computation for a client.

Server Hardware :

Difference Between PCs and Servers

Desktop/workstation is designed for human-to-computer interaction. It is expendable, short-lived and heavily influenced by media, trends, marketing and so on.

A server is designed for computer-to-computer interaction. A server has only one interface to the outside world that matters -- the network interface. A server is designed to be centrally manageable, robust and reliable under high load for years.

Cooling Features: Computers must be kept cool in order to function properly. Servers use devices such as heat sinks and CPU fans to keep components cool, but the case design also plays a vital role in regulating the server's overall temperature.Blade servers however, are the exception. The blade server chassis is responsible for cooling the individual blade servers. For rack mount and tower servers however, the case is specifically designed to keep the server cool.

Filtering: Sometimes fans alone are not enough to keep a server cool. In industrial areas a server’s fans can suck in dust, dirt, soot, and other contaminants. These particles can clog air vents and may also prevent fans from operating efficiently. In order to prevent this type of contamination, some (but certainly not all) server cases are equipped with built in air filters.

A dirty air filter can actually restrict air flow just as badly as if the server’s vents were completely obstructed.

Physical Security: Physical security doesn’t seem to be a major priority when it comes to server case design. Many server manufacturers seem to assume that servers will be placed in physically secure datacenters, so there is little need for physically secure server cases.

Status Indicators: ervers almost always have various forms of status indicators. The status indicators are typically LED lights. Status LEDs are not unique to servers. PCs also use status LEDs. For example, almost every PC has a power indicator and a hard drive activity indicator.

Internal VS. External Storage: An internal drive is, naturally, always powered by the device it's within: your PC, your phone, your tablet. Some external devices contain their own power supplies and plug in independently of the controlling device: most RAID, JBOD, eSATA, and NAS devices do this, either because the data connection doesn't provide power, or because the device needs more power than the interface can provide. Others can be powered by the controlling device. USB hard drives go both ways (computer-powered or self-powered), but memory cards and USB memory sticks are nearly always powered by the controlling device (or a powered hub).

Rack Server : A rack server, also called a rack-mounted server, is a computer dedicated to use as a server and designed to be installed in a framework called a rack.A rack server has a low-profile enclosure, in contrast to a tower server, which is built into an upright, standalone cabinet.The rack server configuration also simplifies cabling among network components. In an equipment rack filled with servers, a special cooling system is necessary to prevent excessive heat buildup that would otherwise occur when many power-dissipating components are confined in a small space.

Tower Server : A tower server is a computer intended for use as a server and built in an upright cabinet that stands alone. The cabinet, called a tower, is similar in size and shape to the cabinet for a tower-style personal computer. This is in contrast to rack server s or blade server s, which are designed to be rack-mounted .

Advantage:

Easier cooling, because the overall component density is fairly low.

Scalability, because an unlimited number of servers can be added to an existing network.

Disadvantages:

Cabling for a large set of tower servers can be complicated.

A group of several air-cooled tower servers in a single location can be noisy because each tower requires a dedicated fan.

Blade Server : It is a server chassis housing multiple thin, modular electronic circuit boards, known as server blades. Each blade is a server in its own right, often dedicated to a single application. The blades are literally servers on a card, containing processors, memory, integrated network controllers, an optional Fiber Channel host bus adaptor (HBA) and other input/output (IO) ports.

Each blade typically comes with one or two local ATA or SCSI drives. For additional storage, blade servers can connect to a storage pool facilitated by a network-attached storage (NAS), Fiber Channel, or iSCSI storage-area network (SAN). The advantage of blade servers comes not only from the consolidation benefits of housing several servers in a single chassis, but also from the consolidation of associated resources (like storage and networking equipment) into a smaller architecture that can be managed through a single interface.

Configuring Server RACK :

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RAID :

RAID (redundant array of independent disks) is a data storage virtualization technology that combines multiple physical disk drive components into a single logical unit for the purposes of data redundancy, performance improvement, or both.

Standard levels

A number of standard schemes have evolved. These are called levels.RAID levels and their associated data formats are standardized by the Storage Networking Industry Association (SNIA) in the Common RAID Disk Drive Format (DDF) standard.

RAID 0

RAID 0 consists of striping, without mirroring or parity. The capacity of a RAID 0 volume is the sum of the capacities of the disks in the set, the same as with a spanned volume. There is no added redundancy for handling disk failures, just as with a spanned volume. Thus, failure of one disk causes the loss of the entire RAID 0 volume, with reduced possibilities of data recovery when compared with a broken spanned volume.

RAID 1

RAID 1 consists of data mirroring, without parity or striping. Data is written identically to two drives, thereby producing a "mirrored set" of drives. Thus, any read request can be serviced by any drive in the set. If a request is broadcast to every drive in the set, it can be serviced by the drive that accesses the data first (depending on its seek time and rotational latency), improving performance.

Sustained read throughput, if the controller or software is optimized for it,

approaches the sum of throughputs of every drive in the set, just as for RAID 0.

RAID 2

RAID 2 consists of bit-level striping with dedicated Hamming-code parity. All disk spindle rotation is synchronized and data is striped such that each sequential bit is on a different drive. Hamming-code parity is calculated across corresponding bits and stored on at least one parity drive.

RAID 3

RAID 3 consists of byte-level striping with dedicated parity. All disk spindle rotation is synchronized and data is striped such that each sequential byte is on a different drive. Parity is calculated across corresponding bytes and stored on a dedicated parity drive.

RAID 4

RAID 4 consists of block-level striping with dedicated parity. This level was previously used by NetApp, but has now been largely replaced by a proprietary implementation of RAID 4 with two parity disks, called RAID-DP.

RAID 5

RAID 5 consists of block-level striping with distributed parity. Unlike RAID 4, parity information is distributed among the drives, requiring all drives but one to be present to operate. Upon failure of a single drive, subsequent reads can be calculated from the distributed parity such that no data is lost. RAID 5 requires at least three disks. RAID 5 implementations are susceptible to system failures because of trends regarding array rebuild time and the chance of drive failure during rebuild. Rebuilding an array requires reading all data from all disks, opening a chance for a second drive failure and the loss of the entire array. In August 2012, Dell posted an advisory against the use of RAID 5 in any configuration on Dell EqualLogic arrays and RAID 50 with "Class 2 7200 RPM drives of 1 TB and higher capacity" for business-critical data.

RAID 6

RAID 6 consists of block-level striping with double distributed parity. Double parity provides fault tolerance up to two failed drives. This makes larger RAID groups more practical, especially for high-availability systems, as large-capacity drives take longer to restore. RAID 6 requires a minimum of four disks. As with RAID 5, a single drive failure results in reduced performance of the entire array until the failed drive has been replaced.

Nested (hybrid) RAID

RAID 0+1:

creates two stripes and mirrors them. If a single drive failure occurs then one of the stripes has failed, at this point it is running effectively as RAID 0 with no redundancy. Significantly higher risk is introduced during a rebuild than RAID 1+0 as all the data from all the drives in the remaining stripe has to be read rather than just from one drive, increasing the chance of an unrecoverable read error (URE) and significantly extending the rebuild window.

RAID 1+0:

reates a striped set from a series of mirrored drives. The array can sustain multiple drive losses so long as no mirror loses all its drives

JBOD RAID N+N

JBOD (just a bunch of disks), it is possible to concatenate disks, but also volumes such as RAID sets. With larger drive capacities, write and rebuilding time may increase dramatically (especially, as described above, with RAID 5 and RAID 6). By splitting larger RAID sets into smaller subsets and concatenating them with JBOD, write and rebuilding time may be reduced. If a hardware RAID controller is not capable of nesting JBOD with RAID, then JBOD can be achieved with software RAID in combination with RAID set volumes offered by the hardware RAID controller. There is another advantage in the form of disaster recovery, if a small RAID subset fails, then the data on the other RAID subsets is not lost, reducing restore time.

Data center

A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems. It generally includes redundant or backup power supplies, redundant data communications connections, environmental controls (e.g. air conditioning, fire suppression) and various security devices.

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