Block Storage Technologies

What is Data Storage ?

Data storage is a general term for archiving data in electromagnetic or other forms for use by a computer or device. ... In addition to forms of hard data storage, there are now new options for remote data storage, such as cloud computing, that can revolutionise the ways that users access data.  

Data storage describes the devices used to hold information. Storage can be considered primary storage or secondary storage, and it is measured in bytes.

Hard Disk Drive

A hard disk drive (HDD), hard disk, hard drive or fixed disk is a data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material.

A hard disk drive (HDD) is a non-volatile computer storage device containing magnetic disks or platters rotating at high speeds. It is a secondary storage device used to store data permanently, random access memory (RAM) being the primary memory device.

A hard disk drive (HDD) is a type of low-cost, high-capacity physical storage used for random-access data in PCs and enterprise data centers.

RAID Levels

The RAID arrays in Cisco storage systems can be configured in various RAID levels. Except where noted below, all RAID levels require a minimum of two disk drives. The levels available are:

RAID 0

RAID level 0 provides data striping. Blocks of data from each file are spread out across multiple disk drives. It does not provide redundancy. This improves the speed of both read and write operations, but does not provide fault tolerance. If one drive fails, all data in the array is lost.

RAID 1

RAID level 1 provides disk mirroring. Files are written identically to two or more disk drives. If one drive fails, the other drive still contains the data. This also improves the speed of read operations, but not write operations.

RAID 4

RAID level 4 provides block level striping similar to RAID level 0, but with a dedicated parity disk. If a data disk fails, the parity data is used to recreate the data on the failed disk. Because there is only one parity disk, this RAID level can slow down write operations.

RAID 5

RAID level 5 provides data striping at the byte level and also stripe error correction information. Parity data, instead of being stored on only one disk, is distributed among all disks in the array. This level provides excellent performance and good fault tolerance. It is one of the most popular implementations of RAID.

RAID 6

RAID level 6 provides block level data striping with parity data distributed across all disks. For additional redundancy, each block of parity data exists on two disks in the array instead of only one. RAID level 6 requires a minimum of four disk drives.

RAID 10

RAID level 10 is a combination of RAID levels 0 and 1. Data is both striped and mirrored. RAID level 10 is used whenever an even number of drives (minimum of four) is selected for a RAID 1 array.

Note: RAID levels 2 and 3 are not available on Cisco storage systems.

Disk Controller and Array Controller

The Disk controller is the controller circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive. Also it provides an interface between the disk drive and the bus connecting it to the rest of the system.

The disk controller is responsible for such drives as the hard drive, floppy disk drive, CD-ROM drive, and any other drive. Today, most disk controllers are found on the motherboard and are either IDE or the newer SATA.

The disk controller is circuitry on the computer's motherboard or on a plug-in circuit board that controls the operation of your hard disk drive, floppy disk drives, or both. When the computer wants to transfer data to or from the disk, it tells the disk controller.

A disk array is a data storage system that contains multiple disk drives and a cache memory. It efficiently distributes data across multiple drives and enables fault tolerance through redundant array of independent disks (RAID).

A disk array is a hardware element that contains a large group of hard disk drives (HDDs). It may contain several disk drive trays and has an architecture which improves speed and increases data protection. The system is run via a storage controller, which coordinates activity within the unit.

Disk arrays are groups of disks that work together with a specialised array controller to potentially achieve higher data transfer and input and output (I/O) rates than those provided by single large disks.

Advanced Technology Attachment 

Advanced Technology Attachment (ATA) is a standard physical interface for connecting storage devices within a computer. ATA allows hard disks and CD-ROMs to be internally connected to the motherboard and perform basic input/output functions.

It is a type of disk drive that integrates the drive controller directly on the drive itself. Computers can use ATA hard drives without a specific controller to support the drive.

Small Computer System Interface

The Small Computer System Interface (SCSI) is a set of parallel interface standards that allows PCs to communicate with peripheral hardware faster than previous interfaces.

SCSI is also frequently used with RAID, servers, high-performance PCs and storage area networks SCSI has a controller in charge of transferring data between the devices and the SCSI bus. It is either embedded on the motherboard or a host adapter is inserted into an expansion slot on the motherboard. 

Fibre Channel Basics 

Fibre Channel, is a high-speed network technology (commonly running at 1, 2, 4, 8, 16, 32, and 128 gigabit per second rates) providing in-order, lossless delivery of raw block data, primarily used to connect computer data storage to servers. Fibre Channel is mainly used in storage area networks (SAN) in commercial data centers. Fibre Channel networks form a switched fabric because they operate in unison as one big switch. Fibre Channel typically runs on optical fiber cables within and between data centers, but can also run on copper cabling.

Fibre Channel Topology

Point-to-Point 

Two devices are connected directly to each other. This is the simplest topology, with limited connectivity.

Arbitrated Loop

In this design, all devices are in a loop or ring, similar to token ring networking. Adding or removing a device from the loop causes all activity on the loop to be interrupted. The failure of one device causes a break in the ring. Fibre Channel hubs exist to connect multiple devices together and may bypass failed ports. A loop may also be made by cabling each port to the next in a ring.

• A minimal loop containing only two ports, while appearing to be similar to point-to-point, differs considerably in terms of the protocol.
• Only one pair of ports can communicate concurrently on a loop.
• Maximum speed of 8GFC.
• Arbitrated Loop has been rarely used after 2010.

Switched Fabric

In this design, all devices are connected to Fibre Channel switches, similar conceptually to modern Ethernet implementations. Advantages of this topology over point-to-point or Arbitrated Loop include:

• The Fabric can scale to tens of thousands of ports.
• The switches manage the state of the Fabric, providing optimized paths via Fabric Shortest Path First (FSPF) data routing protocol.
• The traffic between two ports flows through the switches and not through any other ports like in Arbitrated Loop.
• Failure of a port is isolated to a link and should not affect operation of other ports.
• Multiple pairs of ports may communicate simultaneously in a Fabric.

Fibre Channel Addresses

Port address. Additionally to WWNs there is another addressing scheme that is used in Fibre Channel networks. This scheme is used to address ports in the switched fabric. Each port in the switched fabric has its own unique 24-bit address. 

Fibre Channel Processes

Optional ESP Header (8 bytes): Provides encryption; includes the SPI and ESP sequence number. Optional Network Header (16 bytes): So that you can connect an FC-SAN to non-FC networks. Optional Association Header (32 bytes): Not used by FCP, but can be used to identify processes within a node.

Fabric Shortest Path First

Fabric Shortest Path First (FSPF) is the standard path selection protocol used by Fibre Channel fabrics. The FSPF feature is enabled by default on all Fibre Channel switches. Except in configurations that require special consideration, you do not need to configure any FSPF services.

It s a Link State path selection protocol, similar to OSPF, which is an Interior Gateway Protocol (IGP) widely used in IP networks.This protocol keeps track of the state of the links on all switches in the Fabric.

Zoning

Zoning enables you to set up access control between storage devices or user groups. If you have administrator privileges in your fabric, you can create zones to increase network security and to prevent data loss or corruption. Zoning is enforced by examining the source-destination ID field.

Virtual SAN is a software-defined storage offering from VMware that enables enterprises to pool their storage capabilities and to instantly and automatically provision virtual machine storage via simple policies that are driven by the virtual machine.

VSAN Definition

A virtual storage area network (VSAN) is a logical partition in a physical storage area network (SAN). The use of multiple, isolated VSANs can also make a storage system easier to configure and scale out.

A virtual storage area network (VSAN) is a collection of ports from a set of connected Fibre Channel switches, that form a virtual fabric. Ports within a single switch can be partitioned into multiple VSANs, despite sharing hardware resources.

VSAN trunking enables interconnect ports to transmit and receive frames in more than one VSAN, over the same physical link, using enhanced ISL (EISL) frame format. VSAN trunking is supported on native Fibre Channel interfaces, but not on virtual Fibre Channel interfaces. 

Zoning and VSANs 

Zoning applies only to the switched fabric topology (FC-SW), it does not exist in simpler Fibre Channel topologies. Zoning is different from VSANs, in that each port can be a member of multiple zones, but only one VSAN. VSAN (similarly to VLAN) is in fact a separate network (separate sub-fabric), with its own fabric services .

VSAN Use Cases

Since the introduction of the Cisco MDS 9000 Family, VSANs have provided value to customers and helped them achieve numerous business goals. This section describes the most common solutions based on Cisco VSAN technology.

Internet SCSI 

Internet small computer systems interface (iSCSI) is a networking standard for linking data storage components over a network, usually in storage area networks (SANs). SCSI is an established medium of fast communication between components.




Difference between iSCSI and SCSI
iSCSI is the SCSI protocol mapped to TCP/IP and run over standard Ethernet technologies. This allows Ethernet networks to be deployed as SANs at a much lower TCO than Fibre Channel (FC). Parallel SCSI and serial attached SCSI (SAS) are technologies designed to be inside a box such as DAS or within a storage array.

Block Storage for Cloud Infrastructure 
Block Storage. Centralized storage is integrated into servers as a local hard drive managed by the operating system to enable access to this storage via the local file system.
then they will find block storage to be a common partner for cloud computing. The main disadvantage to SAN environments, where block storage systems are most often found, is the cost and complexity associated with building and managing it.

Block Storage as a Service
The basic resources offered by the Block Storage service are volumes and snapshots which are derived from volumes and volume backups: Volumes. Allocated block storage resources that can be attached to instances as secondary storage or they can be used as the root store to boot instances. 

Understanding Object Storage and Block Storage use cases. Cloud Computing, like any computing, is a combination of CPU, memory, networking, and storage. Infrastructure as a Service(IAAS) platforms allow you to store your data in either Block Storage or Object Storage formats.

Around the Corner: Solid State Drives 
It is not exactly news that hard disk drives are not the only available technology for secondary storage functions, especially if you observe the huge gap of data access latency between main memory (30 to 60 nanoseconds) and HDDs. (3,000,000 to 12,000,000 nanoseconds).

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