DAS RAID NAS SAN

OVERVIEW

•Introduction

•RAID

•DAS

•NAS

•SAN

•Conclusion

INTRODUCTION (1/2)

Everyone knows that the global appetite for data storage is growing at an astonishing rate, that's why traditional storage devices are being not longer reliable in terms of cost, capacity and efficiency

How to cope with the explosive data growth ?

How to store and preserve data while optimizing storage resources?

How to ensure backups?

INTRODUCTION (2/2)

What is a logical drive?

A logical drive :

•is a group of physical disks that appears to your OS as a single drive.

•can comprise one or more disks drives and can use part or all of each disk’s drive capacity.

•it is possible to include the same disk drive in two different logical drives by using just a portion of the space on the disk drive in each.

The combination of multiple disk drive components into a logical unit are made by the mean of a storage technology : RAID

RAID

RAID

In 1987, Patterson, Gibson and Katz at the University of California Berkeley, published a paper entitled “A Case for Redundant Array of Inexpensive Disks(RAID)”.

The basic idea of RAID was to combine multiple, small inexpensive disks drive into an array of disk drives which yields performance exceeding that of a Single, Large Expensive Drive(SLED).

ADVANTAGES OF RAID

Using a RAID storage subsystem has the following advantages:

•Redundancy:• Provides fault-tolerance by mirroring or parity operation.

• Provides disk spanning by weaving all connected drives into one single volume.

•Increased Performance: Increases disk access speed by breaking data into several blocks when reading/writing to several drives in parallel. With RAID, storage speed increases as more drives are added.

•Lower Costs: • Acquiring costs

• Management costs: Floor space Costs, Operational Risk, Lowering Power and Cooling Costs.

FEW TERMS TO UNDERSTAND

•Data Striping: Data is split across multiple drives in a RAID array to form a single logical storage unit. Each drive's storage space is partitioned into stripes, ranging in size from one sector (512 bytes) to multiple megabytes. The stripes then are interleaved so that the logical storage unit is made up of alternating stripes from each drive.

•Mirroring: Used in RAID levels 1 and 1+0 for data recovery. Data is duplicated through mirroring across two disks. If one drive fails, the data remains available on the other disk. It's sort of like low-end clustering.

•Parity: Information Used in RAID levels 3, 4 and 5 for data recovery. In the event of a drive failure, parity information can be combined with the other remaining data to regenerate the missing information.

RAID LEVELS

•Data are distributed across the array of disk drives.

•Redundant disk capacity is used to store parity information, which guarantees data recoverability in case of a disk failure.

•Levels decided according to schemes to provide redundancy at lower cost by using striping and “parity” bits.

•Different cost-performance trade-offs.

RAID 0 : DISK STRIPPING

•Minimum Disks Required=2

•Capacity=N

•Redundancy=No

RAID 0 provides the highest performance but no redundancy.

Data in the logical drive is striped (distributed) across several physical drives.

Performing simultaneous writes

High-Performance applications where data loss is not critical

RAID 1: DISK MIRRORING

•Minimum Disks Required=2

•Capacity=N/2

•Redundancy=Yes

RAID 1 mirrors the data stored in one hard drive to another.

RAID 1 can only be performed with two hard drives.

If there are more than two hard drives, RAID (0+1) will be performed automatically.

Performing simultaneous reads

High Reliability with fast recovery

RAID 0+1: DISK STRIPPING WITH MIRRORING

•Minimum Disk Required=4

•Capacity=N/2

•Redundancy=Yes

RAID (0+1) combines RAID 0 and RAID 1 - Mirroring and Striping. RAID (0+1) allows multiple drive failure because of the full redundancy of the hard drives. If there are more than two hard drives assigned to perform RAID 1, RAID (0+1) will be performed automatically.

RAID 10 is a good choice for general data storage, including serving as a startup drive, and as storage for large files, such as multimedia.

Both performance and reliability are important, e.g. in small databases

RAID 3: DISK STRIPING WITH DEDICATED PARITY DISK•Minimum Disk Required=3

•Capacity=N-1

•Redundancy=Yes

RAID 3 performs Block Striping with Dedicated Parity.

One drive member is dedicated to storing the parity data.

When a drive member fails, the controller can recover/ regenerate the lost data of the failed drive from the dedicated parity drive.

RAID 3 is usually used storing large files, such as multimedia, music, videos, and photos. Performance for writing or reading files larger than 1 MB is dramatically better than in a single-drive, non-RAID system.

RAID 5: STRIPING WITH INTERSPERSED PARITY •Minimum Disk Required=3

•Capacity=N-1

•Redundancy=Yes

RAID 5 is similar to RAID 3 but the parity data is not stored in one dedicated hard drive. Parity information is interspersed across the drive array.

In the event of a failure, the controller can recover/regenerate the lost data of the failed drive from the other surviving drives.

RAID 5 is a good choice for multimedia file storage. Its read speed can be very high, while the write speed is slightly slower, due to the need to calculate and distribute the parity.

FEW TERMS TO UNDERSTAND

•Snapshots: comes in three basic flavors: File system based, subsystem based and volume manager/virtualization based. All three are considerably different. Snapshots are an extremely important function for business continuity, but there are a lot of details to work through. You need a strategy for snapshots as well as a decent understanding of how you will establish operations to work with them. They will change your daily operations and they require constant, ongoing administration. Platform specific operations for flushing cache (file system buffers) matter a whole lot.

•Replication: is the transport of data objects (files -- tables) over a TCP/IP network. The transfer is made from system to system not between storage devices or subsystems.

DAS

DAS

•DAS (Direct Attached Storage) is an architecture for which the storage is “privately” attached to the servers: cannot be shared, it is hard to scale, expensive and complex to manage. 80% of the market it is still DAS

•For an individual computer user, the hard drive is the usual form of direct-attached storage. In an enterprise, providing for storage that can be shared by multiple computers and their users tends to be more efficient and easier to manage.

NAS

NAS 1/2

•NAS is file-level computer data storage connected to an IP network providing data access to a heterogeneous group of clients.

•NAS removes the responsibility of file serving from other servers on the network. They typically provide access to files using network file sharing protocols such as NFS (popular on UNIX systems), SMB/CIFS (Server Message Block/Common Internet File System) (used with MS Windows systems), AFP (used with Apple Macintosh computers), or NCP (used with OES and Novell NetWare).

NAS 2/2

•Easy appliance

•Clustered file-system

•NAS units rarely limit clients to a single protocol

•Not recommended for applications requiring large disk performance

•Heavy usage of CPU

SAN

SAN 1/2

•A Storage Area Network (SAN) is an independent network for storage subsystems, free from the rest of the computer network.

•SAN is a dedicated network that provides access to consolidated, block level data storage.

•It's a networked architecture that provides I/O connectivity between hosts and storage devices.

•SAN devices: hubs, switches, servers and storage devices implements a storage resource environment.

SAN 2/2

The storage network can be:

•A Fiber Channel network• Uses a network of Fiber Channel connectivity devices: FC Switches and Directors

• For transport, an FC SAN uses FCP

• FCP is serial SCSI-3 over Fiber Channel

•Or an IP network• Uses standard LAN infrastructure: Ethernet switches

• For transport, an IP SAN uses iSCSI

• iSCSI is serial SCSI-3 over IP

STORAGE ARRAY

•The concept of a logical volume is very similar to a logical drive. A logical volume is composed of one or several logical drives, the member logical drives can be the same RAID level or different RAID levels.

•The logical volume can be divided into a maximum of 8 partitions. During operation, the host sees a non-partitioned logical volume or a partition of a partitioned logical volume as one single physical drive.

•A Volume Group (VG) is the highest level abstraction used within the Logical Volume Manager. It gathers together a collection of Logical Volumes (LV) and Physical Volumes (PV) into one administrative unit.

FC: FIBRE CHANNEL

•Fibre Channel is a high-speed network technology primarily used for storage networking.

•Despite its name, Fibre Channel signaling can run on twisted pair copper wire in addition to fiber-optic cables.

•It has now become the standard connection type for storage area networks (SAN) in enterprise storage.

•Fibre Channel Protocol (FCP) is a transport protocol (similar to TCP used in IP networks) that predominantly transports SCSI commands over Fiber Channel networks.

FIBRE CHANNEL PROTOCOL LAYERS

FC-0 (Couche Physique)

FC-1 (Encode/Decode)

FC-2 (Framing protocol/Flow

Control)

FC-3 (Common Services)

FC-4 (an interface with one ULP)

IPSCS

IAudio/Video ULP

FC-UL

FC-PH

FC SAN TOPOLOGIES

POINT TO POINT

•This is the simplest topology of the FC SAN, which allows the host and storage to connect directly.

transmitting speed is high

limitation of the system expansion

Host Storage

ARBITRATED LOOP

•One-way loop fashion enables transmitting events between nodes and nodes.

•It’s designed to scale to a limited number of nodes (up to 127).

Low cost (no interconnecting devices needed)

Limited performance (Arbitration overhead and shared bandwidth)

Host

Storage

Storage

SWITECHED FABRIC

•Switched fabric is a computer network topology where many storage devices connect with each other by means of switches.

Bi-directional connection

High performance ( each logical connection receives dedicated bandwidth)

Scalable, robust and reliable architecture

Host

Host

Switch

Switch

Storage

Storage

IP SAN

•IP SAN is the storage area network doing data transmitting processes through TCP/IP protocols. Since the protocol commands are embedded the IP address where the data is transmitted to, IP SAN is the high-efficient and point-to-point storage solution. There are some ways to implement SAN by TCP/IP, such as FCIP (Fiber Channel over IP), iFCP (Internet Fibre Channel Protocol), and the iSCSI (Internet SCSI), which is more cost-efficient than Fibre SAN.

Low acquisition costs

Commodity economics

Utilizing a proven technology installed at almost every business site

Wide area connectivity - no interconnect distance limit

ISCSI

•iSCSI is a internet protocol standards are officially ratified by Internet Engineering Task Force, IETF.

•iSCSI technology simplify the storage area network solution, such as setting time, equipment, and techniques, via the Ethernet interface.

•From the view of the IP SAN topology, hosts are required to receive and process iSCSI IP packages.

ISCSI TOPOLOGY

iSCSI ServeriSCSI Server

iSCSI Server iSCSI Server

iSCSI Tape Library iSCSI Tape Library

iSCSI RAID iSCSI RAID

iSCSI Session

IP Network

ISCSI PROTOCOL MODEL 1/2

Ethernet Header

Ethernet Frame

IP Header

IP Packet (Datagrams)

TCP Header

TCP Segment

PDU Header

PDU Data

Data Data Data

CHK

FCS

ISCSI PROTOCOL MODEL 2/2

SCSI Application

iSCSI Transport

Protocol Services

Interconnect

ServicesTCP

IP

Data

Link

SCSI Application

iSCSI Transport

Protocol Services

Interconnect

ServicesTCP

IP

Data

Link

SCSI Application

Protocol

TargetInitiator

iSCSI Transport

Protocol

IP Network

Interconnect Service Interface

Protocol Service Interface

SAN FC VS SAN ISCSI

FC:

•High cost

•High performance

•Low interoperability

ISCSI:

•Low cost

•Low performance

•Standardized

FC and ISCSI can coexist on a storage network

Each one of them meets different needs

DAS VS NAS VS SAN

DAS NAS SAN

Storage Type Sectors Shared files Blocks

Data

Transmission

IDE/SCSI TCP/IP,

Ethernet

Fiber Channel

Access Mode Clients or

servers

Clients or

servers

Servers

Capacity

(Bytes)

109 109-1012 >1012

Complexity Easy Moderate Difficult

Management

Cost (per GB)

High Moderate Low

CONCLUSION

Choosing the right storage solution is not an easy task especially with such a variety of storage technologies.

that's why, there are several key criteria to consider include:

Capacity: the amount and type of data (file level or block level)

Performance: I/O and throughput requirements

Scalability: Long-term data growth

Availability and Reliability: how mission-critical are your applications?

Data protection: Backup and recovery requirements

Budget concerns