This presentation gives an overview of physical storage technologies and the various ways of accessing storage on a computer or a server. Presented at School of Engineering and Applied Science, Ahmedabad University as a part of Software Engineering course.
2. How is data stored?
• Data that is accessed, modified, or written by a computer
(electronic device) is stored physically using some technology.
• The technology can be:
1. Magnetic Disk Drive
2. Solid State Drive
3. Optical Disk Drive
4. Magnetic Tape Drive
The type of disk used depends on factors like budget, I/O
requirement, longevity, and interface compatibility.
3. Magnetic Disk Drive
• In a magnetic disk drive, data is stored
on magnetic plates which are physically
accessed using a spindle and a
read/write head.
• Each plate is divided into sectors and
tracks.
• Performance measure: RPM, IOPS
4. Solid State Drive
(SSD)
• A solid state drive is made of non-volatile NAND
flash memory which is much faster than magnetic
disk drives.
• There are no mechanically moving parts in an SSD.
An SSD controller manages all I/O operations.
• There are mainly 3 types of SSDs available:
1. Single Level Cell (SLC): 1 bit per flash cell.
Highest performance and longevity but very
expensive.
2. Enterprise-MLC (eMLC): 2 bits per flash cell.
Most commonly used due to strong error
correction.
3. Triple Level cell (TLC): High density and capacity
but low performance and reliability.
5. Direct Attached Storage (DAS)
• Direct Attached Storage is data storage which is physically connected to a
computer using an interface.
• There are many types of interfaces:
1. USB: Rarely used for servers, common for users. 5 Gbps.
2. SATA (Serial AT Attachment): Used for SSDs. Inexpensive. 16 Gbps.
3. PCIe (Peripheral Component Interconnect Express): High performance but
expensive. ~2 GBps.
4. SCSI (Small Computer System Interface): Legacy. Many new standards based
on it. Popular protocol which defines a command set. 5 MBps.
5. SAS (Serial Attached SCSI): Replaced SCSI. Popular due to command set. 12
Gbps.
6. Network Attached Storage (NAS)
• Network Attached Storage is a storage device which is capable of being
accessed over a network.
• The NAS can be connected by a wire (through a server) or wirelessly (USB
ports on Wi-Fi routers/access points).
• It uses file based protocols like SMB (Server Message Block), CIFS
(Common Internet File System), and NFS (Network File System).
• A NAS is generally only accessed like an external drive on a computer
because it is a file-level storage.
• FTP is commonly used with NAS devices.
• E.g.: IETSRV02 (10.20.10.52)
7. Storage Area Network (SAN)
• A Storage Area Network provides block-level data storage to servers.
• A SAN acts just like an internal drive to a server. The processing is handled by a
storage controller (like a Network Interface Card).
• It is not necessary for a SAN to use Ethernet.
• A SAN cannot be accessed directly via a Local Area Network, it uses specific
standards like:
1. FCoE (Fiber Channel over Ethernet)
2. FCSAN (Fiber Channel SAN)
3. iSCSI (Internet Small Computer Systems Interface)
A SAN also allows for advanced features like multipathing, RAID, and storage
virtualization.
