Concept Notes on Data Storage Systems

Concept Notes on Data Storage Systems

Data Sorage can be broadly categorised into : 

1. DAS System

2. NAS systems

3. SAN system 

I. DAS (Direct attached storage) System

This are the conventional storage systems (hard disks etc)  internal in servers

• Storage is directly connected to a single server
  • SCSI, SAS, iSCSI, Fibre Channel 
• DAS systems can be both internal as well as external drives 
• They can be with or without RAID protection 

• Raid types :

  • Software RAID
  • On board RAID on Chip (on Motherboard)
  • Host Adapter based RAID 
• In External drives based DAS systems

• Motherboard has host adapter (HA)
• Storage system is external 
• Controller-based RAID engine 

Internal DAS Advantages

• Low-cost
• Drives are typically included with the server
• Immediate utilization
• Some data protections

External DAS Advantages

• Better than data stored on clients
• Increased availability and performance
• RAID protections
• Increased features and functionality
• Scalability

DAS Disadvantages

• Each server has its own storage device ($$)
• Management is difficult
• Reduced Productivity
• Expensive to backup
• Wasted storage space
• Difficult to share data

II.   NAS Systems 

• Network Attached Storage
• A device that is dedicated to network file sharing.
• NAS is not a network!
• NAS uses LAN or WAN protocols i.e. TCP/IP
• A NAS device can exist anywhere in a LAN or WAN.
• Supported Protocols include CIFS, NFS and HTTP
• NAS does not provide any of the activities that a server in a server-centric system typically provides, i.e. e-mail.
• When an application on the network requests information, the NAS appliance provides file level access, or indexing, to the block layer

Advantages of NAS

• Leverage current networking infrastructure
• Heterogeneous data-sharing environments
• Relatively easy to install and maintain
• Native OS permissions and file locking maintained
• Good performance

Disadvantages of NAS

• A single NAS server can lead to I/O bottlenecks
• Performance penalties

III.  SAN Systems
A storage-area network (SAN) is a dedicated high-speed network (or sub-network) that interconnects and presents shared pools of storage devices to multiple servers. Typically the are in the form of stand alone appliances attached to rack or blade servers. 

Advantages of SAN : 

• High-bandwidth capable of growing incrementally

• Transfers very large blocks of data 

• Offers storage applications such as backup and remote mirroring without bogging down LAN

• Superior performance, reliability and flexible connectivity