What is Open-E DSSv7? 
The Open-E Data Storage Software V7 (DSS V7) is a unified file and block storage management operating system (OS) that provides Network Attached Storage (NAS), iSCSI, InfiniBand and Fibre Channel Storage Area Network (SAN) functionality.

Open-E DSS V7 provides superior performance, security, and scalability at a fraction of the cost of alternative storage offerings. Advanced features of Open-E DSS V7 include Data and Volume Replication, Volume Snapshot, Automatic Failover for iSCSI Volumes, WORM and NDMP. Additionally, Open-E DSS V7supports a wide variety of hardware RAID platforms from the industry's leading names. The versatility of the Open-E DSS V7 also allows users to combine NAS systems with iSCSI SAN systems, and provides built-in virus protection, while enabling the connection of multiple Network Interface Controllers, including Gigabit Ethernet, 10 Gigabit Ethernet, Fibre Channel and InfiniBand. Open-E DSS V7 is easily downloaded to any hardware device for simplified access.
 
GUI ADMINISTRATION
Powerful and Intuitive Web-based User InterfaceThe web-based Graphical User Interface (GUI) of the Open-E Data Storage Software V7 (DSS V7) software makes remote management of the storage device a simple task. By using a web-browser, the DSS can be easily managed from anywhere within the network.

Secured Administration AccessOpen-E DSS V7 is accessed and configured through a web-based, password-protected GUI over Secured Socket Layer (SSL) administration access.

Console ToolOpen-E DSS V7 can be managed by using the console tool. For security reasons some advanced and critical administrator tasks like “removing and restoring volumes and checking and repairing the file system“, can only be managed from the console. Through the console tool, an administrator monitors the status of the network and memory usage, install drivers and hardware and perform other tasks.

Remote Access of Console ToolThe Open-E DSS V7 supports remote access of the console tool enabling management of the server from anywhere in the network.

Tuning ToolsThe performance of the DSS V7 server can be increased by changing the settings of disk, network, file system or network using “Tuning Tools“.

Multiple Management LevelsThe Open-E DSS V7 supports three levels of administrative rights: Full Access, Maintenance and Administration.

Update System (Local or Internet)Update downtime is reduced with the new Update System feature making it possible to reboot from the old system.
 
NETWORK MANAGEMENT
Standard Network Gateway SupportThe Open-E DSS V7 can be used with structured networks in business environments and has an optional data access via Intranet or Internet.

DHCP ClientAssigning IP addresses in a network can be centrally managed and automated through using Dynamic Host Configuration Protocol (DHCP).

Multiple Network Interface Card (NIC) SupportThe Open-E DSS V7 supports usage of two or more network cards to access separate sub-networks or to increase the bandwidth and allows administrators to select services to be enabled on a specified NIC.

Adapter Fault Tolerance (AFT)AFT assures greater reliability by providing a secondary network adapter which automatically takes over, should the primary network adapter fails.

Adaptive Load Balancing (ALB)ALB enhances data throughput by automatically routing data through alternative paths as the application changes.

10 Gb Ethernet with TCP/IP Offload Engine (TOE)To improve the data throughput and latency, the Data Storage Server V7 supports 10 GbE to increase bandwidth, improve overall performance, and reduce message latency across connections. The Open-E DSS V7 supports some 10GbE cards with TCP/IP.

InfiniBand SupportOpen-E supports InfiniBand cards that increase bandwidth, improved overall performance, and reduced message latency across connections.

Proxy SettingsThe Open-E software allows the configuration of the Proxy Server for Internet connections.

IP-SecThe Open-E DSS V7 supports the Secure Internet Protocol (IPsec). This protocol secures data transmitted across a network, preventing confidential and personal information being intercepted or modified.
 
STORAGE MANAGEMENT
Automatic Failover for iSCSI VolumesOpen-E DSS V7 provides fault tolerance via iSCSI Volume Replication. Data is copied in real time to the primary server and every change is immediately mirrored to a secondary server and in the event of a failure of the primary server Open-E DSS V7 automatically switches operations to the secondary server.

New & Improved! Volume ReplicationDSS V7 provides both Synchronous and Asynchronous Volume Replication. Asynchronous Volume Replication is also supported over a WAN with both pair to pair support and multiple sources support.

Cross Data SynchronizationOpen-E DSS V7 synchronizes files and directories from one NAS server to another. Disaster recovery or Disk-to-Disk backup synchronization utilizes block-based data transfer that minimizes network traffic. DSS V7 can synchronize data in both directions: the DSS V7 can be the source and destination of files at the same time, allowing to cross-backup data on several servers.

New & Improved! SCSI-3 Persistent ReservationSupport for persistent reservation commands. This enables support for Windows 2008 and Windows Cluster.

New & Improved! Sys checkEnables you to check the performance of your system.

Hardware and Software iSCSI InitiatorOpen-E DSS V7 supports hardware iSCSI Initiators and has a software iSCSI Initiator for easily expanding the storage capacity of the NAS server. New units and logical volumes can be added by connecting an iSCSI storage system to the NAS server.

Hardware and Software Redundant Array of Inexpensive Disks (RAID) SupportThe Open-E DSS V7 supports Serial Attached SCSI (SAS), SCSI, Serial ATA and IDE controllers of all leading hardware RAID controller manufacturers. The integrated software RAID 0, 1, 5, 6 provides more flexibility and cost savings while creating storage solutions. By mirroring two hardware RAID arrays, the probability of failure can be reduced. The DSS V7 offers highest flexibility in redundancy, performance, costs and storage volume.

Software RAID Degraded ModeThe DSS V7 software boasts a means for creating a RAID when a Hard Disk Drives (HDD) is missing or broken.

E-mail Notification for RAID IssuesEmail alerts are sent to the system administrator in case of issues with the RAID through the DSS software.

Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) SupportThe DSS V7 software includes S.M.A.R.T support for detecting and reporting the status of the Hard Disk Drives (HDD) anticipated on failures.

E-mail Notification for S.M.A.R.T.Email alerts are sent to the system administrator in case of HDD problems through the DSS V7 software.

Multiple Fiber Channel HBA SupportFor higher bandwidth, better latency and performance, the Open-E DSS V7 version supports Fiber Channel HBA's from Emulex, Qlogic and LSI. Fiber Channel is the standard connection type for connecting high speed storage devices to computers in Storage Area Networks (SAN).

Support for over 2TB Physical and Logical Volumes (LV)The Open-E DSS V7 supports logical volumes greater than 2TB and a physical size of up to 16TB in 32bit mode.

SnapshotSnapshot is an immediate point-in-time image of the logical volume. The snapshot image can be used for both consistent and temporary backup, while users still have uninterrupted and complete access to the LV. Files can be recovered from previous snapshots should a file be accidentally deleted or modified.

Multiple Snapshots with Scheduling FunctionThe Open-E DSS V7 supports Multiple Snapshot with Scheduling to create snapshots at predefined points in time (e.g. automatically every hour).

Multiple Logical Volume & GroupsLogical volume groups allow storage administrators to create logical storage pools that span multiple physical disk drives. With its support of multiple logical volume groups, the Open-E DSS V7 makes it easier to meet the changing needs of users and applications while making the maximum use of available physical disk space.

Online Logical Volume ExpansionOnline logical volume expansion allows administrators to change the size of storage volumes as needed without having to restart the application, recreate the volume, and backup and restore data to the volume.

Support for Online Capacity ExpansionA hardware RAID controllers expansion capability supports the increase of size of existing units without removing data.
 
MONITORING
Hardware MonitoringOpen-E DSS V7 monitors hardware status such as temperature, voltage and fan speed provided by the motherboard's sensors.

Simple Network Management Protocol (SNMP) (v2 & v3)The DSS V7 uses SNMP for monitoring data throughput, Central Processing Unit (CPU) and Random Access Memory (RAM) usage to name a few.

Email NotificationIn the event of a technical failure of the storage device, administrators are alerted by Email.

Log FunctionThe Open-E log file is an effective instrument in analyzing and solving technical issues.
 
HARDWARE SUPPORT
Uninterruptible Power Supply (UPS) SupportA UPS eliminates the effects of a temporary power outage and provides a safe shutdown, without loss of data, in case of power failure. The UPS device can be connected by Communications Port (COM-port) or Universal Serial Bus (USB) to the server.

Network UPS SupportThe DSS V7 is capable of using the Simple Network Management Protocol (SNMP) interface for communication with other SNMP-enabled servers (e.g. Open-E DSS) for a smooth server shutdown in the event of a power failure. The server with the UPS sends a power failure signal through the network to other servers (in slave mode) and will shut down all servers in the network.
 
SPECIFIC NETWORK ATTACHED STORAGE (NAS) FUNCTIONALITY
Windows Active Directory / Primary Domain Controller SupportOpen-E DSS V7 supports Windows Active Directory (AD), Primary Domain Controller (PDC), Lightweight Directory Access Protocol (LDAP) and AD & NIS User-/Group ID synchronization to leverage information about users, groups, systems and other resources stored in the Active Directory. The support of Access Control List (ACL) ensures that access rights of users are automatically taken over from the Domain.

Support for Network Information Service (NIS)The Open-E DSS V7 supports NIS for easier and consistent access of information stored on any other data storage server using NIS directory service protocol by enabling distribution of system configuration data such as user and host names between computers on a computer network.

File System with Journaling SupportJournaling support makes the file system more reliable and allows easier, faster recovery from unexpected shutdowns.

User and Group Quota ControlAdministrators can control users with large disk requirements by assigning a dedicated share or by restricting their individual usage through individual user quotas or to assign a quota to a group to which the user belongs.

Antivirus (server's shares scanning)Open-E DSS V7 has an integrated Antivirus software tool for scanning shares on viruses at predefined points in time. The Virus Definition Database can be updated and is stored on the NAS device.

Antivirus (online scanning)The Data Storage Software V7 also supports online scanning of files transferred via the SMB and FTP protocol.

USB Storage Support for Dynamic DiskUSB Units connected to DSS V7 can be used as a Dynamic Units – which can be easily used for local backups.

Backup-Agents (Veritas, EMC Dantz, CA BrightStor) SupportOpen-E DSS V7 backup agents help administrators to backup and protect data on NAS servers with backup software from Veritas, Dantz, or CA BrightStor ARCserve thus improving data transfer, network security and real-time directory browsing, monitoring tasks and supporting cross-platform backup support.

Supported Network Clients and Network File ProtocolOpen-E DSS V7 supports the file based protocols CIFS (Common Internet File System)/SMB, NFS (Network File System), FTP (File Transfer Protocol), FTPS and Apple Talk enabling Windows, Linux, Unix and Macintosh clients to share data on the same server.

External Lightweight Directory Access Protocol (LDAP)The Open-E DSS V7 supports external LDAP enabling administrators to configure and manage multiple DSS V7 systems from one single point (either an Open-E software with a LDAP database or any other LDAP server).
 
SPECIFIC iSCSI FUNCTIONALITY
Multiple Challenge Handshake Authentication Protocols (CHAP) per TargetIn Open-E DSS V7, CHAP users can be assigned to a specific iSCSI target. CHAP is an authentication schema, managed by user name and password, to validate the identity of users to manage the access rights of users to targets.

MPIO SupportThe Open-E DSS V7 allows set multiple connections to one target increasing performance and reliability.
 
BACKUP FUNCTIONALIY
Task Mechanism with SchedulingManagement of all the tasks is much easier and convenient using the unified task mechanism with scheduling for data and volume replication, backup and snapshot. Tasks are scheduled as to when to activate and may have many schedules.

Virtual TapesConfigure tape drive emulation on share or Dynamic Volume (e.g. dynamically attached hard drive) backup for tape drives is the same as backup on virtual tapes.

WormWorm provides Write Once Read Many functionality for data archiving.

NDMP 4.0Network Data Management Protocol defines a network-based mechanism and protocol for controlling backup, recovery, and other data transfers between primary and secondary storage devices.

Tape Library SupportAutomate backups with use of tape drive libraries.

Internal DatabaseMaintain all backup files including backup history.

Tape Retention TimeSet schedule for tapes to be rewritten for new backup.
 
OTHER
SWAP SupportSWAP is used to store memory areas on hard drives instead of Random Access Memory (RAM). The DSS software dumps memory to SWAP in case of additional memory is need (e.g. repairing the file system after a degraded RAID).

Liquid Crystal Display (LCD) Panel SupportOpen-E DSS V7 supports single, dual, multiple or pyramid LCD display configuration.

One License per Storage DeviceRegardless of the number of users connected to the storage device, Open-E license schema is a one license per DSS V7 and is priced accordingly. Whether you have 5, 500, 15,000 or more, you only pay one price for one Data Storage Software V7 License.

Superuser FunctionA "Superuser" account has unrestricted access to all the files and volumes and is an especially helpful feature when certain directories or files are no longer accessible.

Local Backup on Dynamic UnitsThrough the DSS V7, a local HDD or a USB drive can be defined as a Dynamic Unit and acts like a normal tape drive which can backup the NAS server and be removed without shutting down the server.

Cross Data SynchronizationOpen-E DSS V7 synchronize files and directories from one NAS server to another. Disaster recovery or Disk-to-Disk backup synchronization utilizes block-based data transfer that minimizes network traffic. DSS V7 can synchronize data in both directions: the DSS V7 can be the source and destination of files at the same time, allowing to cross-backup data on several servers.

Target Password SupportOpen-E DSS V7 allows set up password for iSCSI targets to protect them from unauthorized access.

Read Only Logical Unit Number (LUN)This function allows the user to set the LUN as a read-only device (for iSCSI Target only).

What's Windows Storage Server 2012 R2?
Windows® Storage Server 2012 R2 is a dedicated file and print server based on Windows Server 2012 R2 that is designed for dependability, seamless integration, and best value in networked storage. Windows Storage Server 2012 R2 integrates with existing infrastructures and supports heterogeneous file serving as well as backup and replication of stored data. Windows Storage Server is also an ideal solution for consolidating multiple file servers into a single solution that enables cost reduction and policy-based management of storage resources.
Using the power of Windows Server 2012 R2, Windows Storage Server 2012 R2 helps organizations store and protect valuable end user data. From branch office file serving to full data center integration, Windows Storage Server 2012 R2 is the dependable and scalable choice in storage. The hardware is easy to install and manage, and offers a wide array of features that simplify file serving and the backup and replication of stored data.
Windows Storage Server 2012 R2 includes advanced availability features such as point-in-time data copies, replication1, and server clustering. Because Windows Storage Server 2012 R2 solutions are preconfigured, they can be deployed out of the box in minutes. Windows Storage Server 2012 R2 integrates with existing infrastructures, so enterprises can make full use of commonly-used network environments and standard management software, as well as the Active Directory® service. Preconfigured Windows Storage Server 2012 solutions are available in sizes ranging from a few terabytes to several hundred terabytes.
Windows Storage Server 2012 R2 Features:
Dependable
FeatureBenefitHigh reliability


Windows Storage Server 2012 R2 is a dedicated file and print server that has all functionality unrelated to file serving removed, increasing reliability and lowering the overhead on the device CPU. Built-in hardware redundancies are included in most solutions to provide a fully redundant architecture.

Availability


Windows Storage Server 2012 R2 makes possible the creation of high availability solutions with native support for multiple node (up to eight) failover clustering. With support for MPIO from host to storage, high availability solutions at the data transport level can also be implemented. Combining these features with the Distributed File System (DFS) can help ensure availability at the file and physical device level.

Fast data recovery


Using the Shadow Copy of Shared Folders feature, you can restore deleted or corrupted files within minutes, instead of the hours it can take to restore from tape. Built on VSS, this feature can store up to 64 point-in-time copies per volume and allows end users to recover previous versions of files.

Replication


Windows Storage Server 2012 R2 allows you to increase data availability and provide disaster recovery by creating multiple copies of data on remote servers over local area networks (LANs) or wide area networks (WANs) using an integrated technology solution.


 
Integrates Seamlessly
FeatureBenefitIntegrates seamlessly into IT infrastructure


Windows Storage Server 2012 R2 includes heterogeneous support for protocols such as SMB, NFS, AppleTalk, and Netware, allowing data to be shared among different platforms. In addition, native integration with the Active Directory® service avoids any need to make network changes when deploying Windows Storage Server 2012 R2 storage devices.

Integrates with existing IT investments


Windows Storage Server 2012 R2 is fully compatible with server management tools such as Microsoft Systems Management Server, Tivoli, and HP OpenView, as well as popular antivirus software, allowing you to get the most out of current investments. The hardware also integrates natively with Active Directory, enabling the use of Group Policy objects, Kerberos authentication, and Encrypting File System (EFS) to preserve data security.

Integrates with SANs


A Windows Storage Server 2012 R2 device can integrate with a SAN by acting as a gateway to the SAN. Support for SANs in Windows Server 2012 R2 includes remote boot, flexible volume mounting, and an enhanced driver model to support SAN deployment scenarios.

iSCSI support


Windows Storage Server 2012 R2 supports the iSCSI protocol, making it easy to integrate with IP data transport environments.

 
Best Economics
FeatureBenefitLow acquisition and installation costs


Windows Storage Server 2012 R2 makes possible some of the lowest cost per gigabyte solutions in the industry. These solutions can be deployed in minutes by using the Windows user interface to connect to the network, join an Active Directory domain or local workgroup, add users, create shares, or select file sharing protocols.

Low total cost of ownership (TCO)


Consolidating multiple file servers onto a single device reduces server management overhead and associated IT staff costs. Devices can be remotely managed using a simple user interface, simplifying maintenance and providing centralized control of processes like backups, restores, and upgrades.

Scalable solutions to grow with your business


Windows Storage Server 2012 R2 enables IT administrators to easily manage growing amounts of data and to take advantage of high scalability to expand storage capacity as needed. With this scalability, a “pay as you grow” strategy can be implemented to ensure the efficient use of storage hardware resources.

What's iSCSI?
iSCSI is Internet SCSI (Small Computer System Interface), an Internet Protocol (IP)-based storage networking standard for linking data storage facilities, developed by the Internet Engineering Task Force (IETF). By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. The iSCSI protocol is among the key technologies expected to help bring about rapid development of the storage area network (SAN) market, by increasing the capabilities and performance of storage data transmission. Because of the ubiquity of IP networks, iSCSI can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.
How does iSCSI work?
When an end user or application sends a request, the operating system generates the appropriate SCSI commands and data request, which then go through encapsulation and, if necessary, encryption procedures. A packet header is added before the resulting IP packets are transmitted over an Ethernet connection. When a packet is received, it is decrypted (if it was encrypted before transmission), and disassembled, separating the SCSI commands and request. The SCSI commands are sent on to the SCSI controller, and from there to the SCSI storage device. Because iSCSI is bi-directional, the protocol can also be used to return data in response to the original request.
iSCSI is one of two main approaches to storage data transmission over IP networks; the other method, Fibre Channel over IP (FCIP), translates Fibre Channel control codes and data into IP packets for transmission between geographically distant Fibre Channel SANs. FCIP (also known as Fibre Channel tunneling or storage tunneling) can only be used in conjunction with Fibre Channel technology; in comparison, iSCSI can run over existing Ethernet networks. A number of vendors, including Cisco, IBM, and Nishan have introduced iSCSI-based products (such as switches and routers).
Role of iSCSI
iSCSI is a data transport protocol used to carry block-level data over traditional Ethernet networks and the Internet. The term iSCSI stands for Internet SCSI or Internet Small Computer Systems Interface. SCSI itself is one of the oldest and most common protocols used to transfer blocks of data over short distances, typically between a server’s applications and the storage devices - - such as, disk drives - - that are directly attached to that server.a
iSCSI builds on the SCSI protocol by encapsulating SCSI commands and allowing these encapsulated data blocks to now be transported at an unlimited distance, via TCP/IP packets over traditional Ethernet networks.
The iSCSI protocol describes how blocks of data are to be transmitted between “initiators” on an Ethernet network and their storage “targets”. The following section further describes the role of initiators, targets and the iSCSI components typically required for an initial IP SAN implementation.
An initiator is typically a server hosting an application, where the application makes periodic requests for data to a related storage device. Initiators are also referred to as servers or host computers. The iSCSI device driver that resides on the server may also be called an initiator.
Initiators “initiate” (or begin) iSCSI data transport transactions by making an application request to send/receive data either to or from one or more storage devices. The application request is immediately converted into SCSI commands, then encapsulated into iSCSI where a packet and header are added for transport via TCP/IP over either the Internet or traditional Ethernet networks.
Targets are one or more storage devices that reside on the network. Targets receive iSCSI commands from various initiators (or servers) on the network. On the target’s side, these commands are then broken down into their original SCSI format to allow block data to be transported between the initiator and the storage device.
The target will respond to a server’s data request by sending SCSI commands back to that server. These commands are again encapsulated via iSCSI for transport over the Ethernet. Targets can be any type of storage device, such as a storage array that is part of a larger IP-based storage area network, or IP SAN. They could also be a separate tape library residing on either the SAN or elsewhere on the network. 

What's RAID?
RAID - Redundant Array of Inexpensive (or sometimes "Independent") Disks - is a method of combining several hard drives into one logical unit. It can offer fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives.
RAID is a mature technology that speeds up data access while at the same time protecting your data from hard disk failure. RAID is quickly becoming a necessary component in every network since data loss and downtime can prove both fatal and financially destructive. Most networks are designed to provide instant access to massive amounts of data. More and more employees have to access customer and other databases. Intranets and corporate Web sites provide access to huge databases online.
Benefits of RAID
RAID provides increased storage capacities, and protects your important data from hard drive failure. 


There are multiple benefits of using RAID:

• Reliability
• Scalability
• Real-time data recovery with uninterrupted access when a hard drive fails
• System uptime and network availability
• Protection against data loss
• Multiple drives working in parallel increase system performance

A disk system with RAID capability can protect its data and provide on-line, immediate access to its data, despite a single disk failure (some RAID storage systems can withstand two concurrent disk failures). RAID capability also provides for the on-line reconstruction of the contents of a failed disk to a replacement disk.
RAID offers faster hard drive performance and nearly complete data safety. Storage requirements are expanding as file sizes get bigger and rendering needs get more complex. If you handle very large images or work on audio and video files, faster data throughput means enhanced productivity. RAID can be backed up to tape while the system is in use.
RAID Levels
The most common RAID levels, listed below, each exhibit their own unique benefits and drawbacks. This overview will attempt to highlight each or help you find the right RAID level for your particular application. Please note that the numbers assigned to each level of RAID are not indicative of superiority, they are merely for differentiation.

• RAID 0
• RAID 1
• RAID 5
• RAID 10
• RAID 50

 
RAID 0 (STRIPING)
RAID 0 refers to striping data across multiple disks without any redundant information. Data being written to the array is broken down into blocks(stripes) and distributed sequentially across the member disks of the array. This level is also referred to as pure striping. This type of array provides hign I/O performance at low inherent cost but provides no redundancy of Fault Tolerance. Because the data is not stored contiguously on a single drive, it can be accessed in parallel - that is to say the pieces of data are read back from multiple sources near simultaneously. Unfortunately, striping reduces the level of data availability since a disk failure will cause the entire array to be inaccessible. RAID 0 was not defined originally but has become a commonly used term.

• Minimum number of drives required: 2

Recommended Applications

• Video Production and Editing
• Image Editing
• Pre-Press Applications
• Any application requiring high bandwidth

Advantages

• High performance
• Very simple design. Easy to implement
• No parity overhead
• No capacity loss - all storage is usable

Disadvantages

• Not a "true" RAID due to the lack of fault-tolerance
• Failure of a single drive will result in loss of all data on the array
• Should never be used in mission critical environments

RAID 1 (MIRRORING / DUPLEXING)
RAID 1 is the first defined level that allows a measure of data redundancy. Data written to one disk drive is simultaneously written to another disk drive. If one disk fails, the other disk can be used to run the system and reconstruct the failed disk. Since the disk is mirrored, it does not matter if one of them fails because both disks contain the same data at all times. RAID level 1 provides high data availability since two complete copies of all information are maintained. In addition, read performance may be enhanced if the array controller allows simultaneous reads from both members of a mirrored pair. Higher availability will be achieved if both disks in a mirror pair are on separate I/O busses, known as duplexing.

• Minimum number of drives required: 2

Recommended Applications

• Accounting
• Payroll
• Financial
• Any application requiring very high availability

Advantages
 

• One Write or two Reads possible per mirrored pair
• Twice the Read transaction rate of single disks, same Write transaction rate as single disks
• Fault tolerant 
• Transfer rate per block is equal to that of a single disk
• Easy to recover data in case of drive failure  100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk. Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures
• Easy to implement
• Higher read performance than a single disk
• Simplest RAID storage subsystem design

Disadvantages

• Inefficient - 100% parity overhead is the highest of all RAID types.
• Becomes very costly as number of disks increase, it requires twice the desired disk space
• Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended
• May not support hot swap of failed disk when implemented in "software"

RAID 5 (STRIPING AND PARITY)
RAID 5, similar to level 3, stripes data and parity to generate redundancy. However, instead of requiring entirely new disk for parity storage, the parity is distributed through the stripe of the disk array. In RAID 5 both parity and data are striped across a set of separate disks. Next, the new parity is calculated. Finally, the new data and parity are written to separate disks. Data chunks are much larger than the average I/O size, but are still resizable. Disks are able to satisfy requests independently which provides high read performance in a request rate intensive environment. Since parity information is used, a RAID 5 stripe can withstand a single disk failure without losing data or access to data.

• Minimum number of drives required: 3

Recommended Applications

• File and Application servers
• Database servers
• WWW, E-mail, and News servers
• Intranet servers
• Most versatile RAID level

Advantages
 

• High efficiency - highest read data transaction rates, Medium Write data transaction rates
• Good aggregate transfer rate
• Cost effective - only 1 extra disk is required
• Fault tolerant
• Low ratio of ECC (Parity) disks to data disks means high efficiency
• The best choice in multi-user environments which are not write performance sensitive.

Disadvantages

• Disk failure has a medium impact on throughput
• Most complex controller design
• Difficult to rebuild in the event of a disk failure (as compared to RAID level 1)
• Individual block data transfer rate same as single disk

RAID 0+1
RAID 10 is technically (RAID 1 + RAID 0), a combination of RAID 1 and 0 - mirroring and striping, but without parity. RAID 10 is a stripe across a number of mirrored drives. It is implemented as a striped array whose segments are RAID 1 arrays. RAID 10 has the same fault tolerance as RAID level 1, as well as the same overhead for fault-tolerance as mirroring alone. Advantages: Very high I/O rates are achieved by striping RAID 1 segments Excellent solution for sites that would normally use RAID 1 Great for Oracle and other databases which need high performance and fault tolerance.

• Minimum number of drives required: 4

Advantages
 

• Fault tolerant
• Very High I/O rates

Disadvantages

• Very expensive - Expensive to maintain As with Raid 1 total capacity is equal to half of the total capacity of all disk in the array
• High overhead
• Very limited scalability

RAID 10
NOT to be confused with RAID 0+1, RAID Level 10 is a striped (RAID 0) array whose segments are mirrored (RAID 1). It is similar in performance to RAID 0+1, but with better fault tolerance and rebuild performance. It has the same fault tolerance as RAID level 1 with the same overhead for fault tolerance as mirroring alone. This RAID level is a combination of RAID 1 (mirroring) and RAID 0 (striping), having both features of these arrays - security and sequential performance. Typically four plus hard drives are used, because RAID 10 creates two pairs of mirrored arrays and combines these arrays to form one RAID 0 array. RAID 10 is especially appropriate for redundant storage of large files, and because parity is not calculated, write operations are very fast.

• Minimum number of drives required: 4

Recommended Applications

• Database server requiring high performance and fault tolerance

Advantages
 

• High fault tolerance
• High I/O rates achieved by striping RAID 1 segments
• Faster rebuild performance than RAID 0+1
• Under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures
• Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost

Disadvantages

• Very expensive
• High overhead
• All drives must move in parallel to proper track lowering sustained performance
• Very limited scalability at a very high inherent cost

RAID 50
RAID Level 50 is a striped (RAID 0) array which is striped across a RAID 5 array. Performance is improved compared to RAID 5 because of the addition of the striped array. Fault tolerance is also improved.

• Minimum number of drives required: 6

Advantages
 

• Higher fault tolerance than RAID 5
• Higher efficiency than RAID 10
• Higher I/O rates

Disadvantages

• Very complex and expensive to implement

What's NAS?
A network-attached storage (NAS) device is a server that is dedicated to nothing more than file sharing.
NAS does not provide any of the activities that a server in a server-centric system typically provides, such as e-mail, authentication or file management.
NAS allows more hard disk storage space to be added to a network that already utilizes servers without shutting them down for maintenance and upgrades.
With a NAS device, storage is not an integral part of the server. Instead, in this storage-centric design, the server still handles all of the processing of data but a NAS device delivers the data to the user.
A NAS device does not need to be located within the server but can exist anywhere in a LAN and can be made up of multiple networked NAS devices. 

Why NAS?
Network-attached storage (NAS) is hard disk storage that is set up with its own network address rather than being attached to the department computer that is serving applications to a network's workstation users. By removing storage access and its management from the department server, both application programming and files can be served faster because they are not competing for the same processor resources. The network-attached storage device is attached to a local area network (typically, an Ethernet network) and assigned an IP address. File requests are mapped by the main server to the NAS file server.
Network-attached storage consists of hard disk storage, including multi-disk RAID systems, and software for configuring and mapping file locations to the network-attached device. Network-attached storage can be a step toward and included as part of a more sophisticated storage system known as a storage area network (SAN).
NAS software can usually handle a number of network protocols, including Microsoft's Internetwork Packet Exchange and NetBEUI, Novell's Netware Internetwork Packet Exchange, and Sun Microsystems' Network File System. Configuration, including the setting of user access priorities, is usually possible using a Web browser. 

Differentiating between NAS, DAS and SAN
A NAS Appliance does just one thing - providing vast amounts of storage accessible from your network at the lowest TCO (total cost of ownership).
NAS is distinguished from DAS (Directly Attached Storage) in that the storage is accessed on another "box" through the network, instead of via direct SATA or SCSI cabling.
SAN means Storage Area Network, and is the overall space in which servers and workstations are able to access storage across the network from NAS appliances.
NAS has many advantages over DAS, such as its modularity - you can keep adding NAS appliances to your network almost indefinitely without having to add new servers, whereas you can practically only add a small number of DAS boxes to a single server.