Failover at multiple level in storage networks

Storage networks can be broadly classified into 3 levels and the fail over or Redundancy feature is very important aspect of IT storage business and it is implemented in every interconnecting components in the networks.
Host or Server(s) Level
Network Level
Storage sub-system(s) Level

Fail-Over:
If the data passage path of any of the component in the storage networks fails, the auto-mechanism that provides an alternate path instantly to avoid the data loss is called fail-over.
Example: If a component such as a RAID controller module or a cable fails, or an error occurs on the data path to the preferred RAID controller module, virtual disk ownership is moved to the alternate non preferred RAID controller module for processing. This failure or error is called failover.

Host or Server Level:
Hosts or servers are associated with few interconnect peripherals such as Host Bus Adapter [HBA], Ethernet adapters et al. some common fail-over feature implementations that you see is at the HBA device in the form of Fail-over driver such as MPP or MPIO [Multi Path driver].
Another stage of fail-over implementation could be to the entire host or server in the form of Clustering, Microsoft Clustering or Linux or Solaris or Unix clustering.

Network Level:
At Switches or Routers, we can provide fail-over by connecting one port or path of the servers & storage sub-systems to one switch port & another port or path connected through another switch port. thus we need at the least two switches to handle the Preferred path & Alternative path of data passage.
usually such setups are know as High Availability Fail-over setup.

Sub-system Level:
Within the SAN storage sub-systems, there are multiple components such as RAID Processors or controllers, Hard disks, Drive trays, power supplies et al.
At Hard disk level , RAID & Hot sparing is used in co-operation with RAID processors as fail-over.
At Drive tray or Enclosure level, there will be dual Service Modules that act as fail-over.
At the RAID Processor or Controller level, there will be Dual RAID processors or Controllers that provide fail-over mechanism.

Fail-over is very vast concept and there are plenty of ways to implement it at different components of the storage networks. for more information you can always buzz me on Email.

Web based Storage & Virtualization Training

NOTE: this blog post is borrowed from other sites. just for the sake of readers request " FAQ: any training centers available in storage in Bangalore?".
Learning through Videos is the fastest & most effective method after learning from an instructor or a personal trainer. Cost of a personal trainer is high to learn Storage technology hence a team I know very well is developing a website for Storage fundamentals + SAN training using Videos. Learning from Videos that too Web based videos has advantages like
- you learn at your own pace,
- you replay the video & see it number of times to perfect the concept or technology

A separate website is being developed by a team of Storage professionals who will be Sharing some of their industry experiences,
Giving you tips for a Career in Storage technology
But main focus will be to give you a Strong Fundamental knowledge on Storage technology

The topics covered will be around(This is just the initial list I got they promised that it will grow more soon, lot more will be covered)
Storage Basics
SAN(Storage Area Network): SAN components
SAN Hardware
SAN Software
SAN Configuration & Troubleshooting overview
iSCSI (SCSI over IP)
FC (Fibre Channel)
Storage connectivity & interfaces:SCSI,SAS,SATA & more.


There will be huge bonus additional Videos & materials like
- What to expect in Storage job interviews
- Tips to prepare your resume to get more interviews from Storage companies
- Tips for interview preparation for Storage technology job openings
- Tips for prioritizing what to give importance & which topics you need to perfect
- You will receive 300+ interview questions from different Storage company interviews which itself is valued at $100. You get this free when you join for this Video training membership website.

Cost for this web based training access will be $500 (USD) payable through paypal or credit card. Those who are interested please email semiconsys@gmail.com today & confirm your interest. The access to this membership based website will be limited only to few since the website development team wants to work more closely with the members & provide some additional value adds, hence I would recommend you to email today & confirm your interest to join.

You will soon get to see a preview Video from their list of Storage Technology Videos on this blog. You will also see lot more updates about this new website being developed soon on this blog.May be I will post some of the reviews or Videos from members who joined & benefited from this web based training website.

Storage Subsystems - implementation in SAN

********If anyone need expert consultation, do send me email at storagetrendz@gmail.com************************

* The storage components of a SAN are the storage arrays. Storage arrays include storage processors (SPs). The SPs are the front end of the storage array. SPs communicate with the disk array (which includes all the disks in the storage array) and provide the RAID/LUN functionality.
* Storage Processors or Controllers:
SPs provide front-side host attachments to the storage devices from the servers, either directly or through a switch. The server HBAs must conform to the protocol supported by the storage processor. In most cases, this is the FC protocol.
* Storage processors provide internal access to the drives, which can be using a switch or bus architecture. In high-end storage systems, drives are normally connected in loops.
* This back-end loop technology employed by the SP provides several benefits:
# High-speed access to the drives
# Ability to add more drives to the loop
# Redundant access to a single drive from multiple loops (when drives are dual-ported and attached to two loops)
* Storage Devices
Data is stored on Hard disk arrays or tape devices (or both).
Disk arrays are groups of multiple disk devices and are the typical SAN disk storage device. They can vary greatly in design, capacity, performance, and other features.
* storage array uses RAID (Redundant Array of Independent Drives) technology to group a set of drives.
* A LUN is a single unit of storage. A LUN is also known as a volume or Virtual Disk or a logical drive, A RAID Group is one or more LUNs with specific RAID level defined.
* Most storage arrays provide additional data protection and replication features such as
snapshots, Clone copies and Remote mirroring.
# A snapshot is a point-in-time copy of a LUN. Snapshots are used as backup sources for the overall backup procedures defined for the storage array.
# Clone copies are actual copy of a LUN, it allows data movement from one LUN to another for an additional copy for testing.
# Remote mirroring provides constant synchronization between LUNs on one storage array and a second, independent (usually remote) storage array for disaster recovery.

RAID Storage Concept unleashed - Part 1

Basic Form of storage devices are Hard disk, Tapedrive, Flash memory,CD,DVD,Pen drives, Tape Libraries, JBOD, Enclosurs, Storage RAID Arrays & so on and the major Players of this business are IBM, HP, Hitachi, Seagate, Maxtor, Fujitsu, StorageTek, Toshiba, Intel, Sun, EMC2, Netapp etc...
Innovation continued with sense of grouping mupltiple Storage devices together in order to increase total available space for stoage and hence JBOD (Just Bunch of Disks) boxes are designed. (JBOD is a storage box containing mulptiple Hard disks and when connected to server or host, server assumes it as single disk and stores data).
JBOD's usage is limited by its design because aprat from combining multiple drives it does not give any further inteligence (dumb box). now emphasis was on adding inteligence to the JBODs and hence Enclosures came into existence with RAID (redundant array of independent disks) implementations.
With the Design & implementation of RAID concepts in the form of different RAID levels (RAID0,RAID1,RAID2,RAID3,RAID4,RAID5,RAID6,RAID0,RAID10,RAID01,RAID50 and so on), storage technology started exploring new dimensions of growth. Storage technology together with Server technology & Networking technology heralded the Design and implementation of Direct Attacted storage, Storage Area Network and Network attached Storage.
Storage devices (Hardware) have seen major changes in the form of innovations and also software in the form of management softwares, Configuration softwares, Backup softwares, Volume manager softwares, Virtualization softwares and so on have equally contibuted to implement complex form of solutions and at present existing Storage technologies (Hardware & Software) are driving the Data management business.

The term RAID was first defined in paper published by David A. Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley in 1987. RAID (Redundant Array of Independent Disks) is a technology for managing how data is stored on the physical or hard disks that reside in your system or are attached to it.
To understand RAID, you must understand fundamental terms such as physical drive, physical array, Logical Drive or Volume and logical Arrays.
Physical Drive: Physical drives are typically indivisual Hard disks that are connected to Server (Host)
Physical Array: One or more physical drives are collected together to form a physical array (JBOD, Enclosures, Storage Arrays).
Logical Arrays: Logical arrays are formed by splitting or combining physical arrays. Typically, one logical array corresponds to one physical array. However, it is possible to set up a logical array that includes multiple physical arrays (typically used to allow multiple RAID levels). It is also possible to set up two entirely different logical arrays from a single physical.
Logical Drives: One or more logical drives are formed from one logical array (much the same way they would normally be formed from one physical drive in a non-RAID system). These appear to the operating system as if they were regular disk volumes, and are treated accordingly, with the RAID controller managing the array(s) that underlie them.

To Implement RAID, you must uderstand fundamental concepts of RAID such as Striping, Mirroring, Parity & Spanning.
Mirroring: Mirroring is one of the two data redundancy techniques used in RAID (the other being parity). In a RAID system using mirroring, all data in the system is written simultaneously to two hard disks instead of one; thus the "mirror" concept. The principle behind mirroring is that this 100% data redundancy provides full protection against the failure of either of the disks containing the duplicated data. Mirroring setups always require an even number of drives for obvious reasons.
The chief advantage of mirroring is that it provides not only complete redundancy of data, but also reasonably fast recovery from a disk failure. Since all the data is on the second drive, it is ready to use if the first one fails. Mirroring also improves some forms of read performance (though it actually hurts write performance.)
The chief disadvantage of RAID 1 is expense: that data duplication means half the space in the RAID is "wasted" so you must buy twice the capacity that you want to end up with in the array. Performance is also not as good as some RAID levels.
Mirroring is used in RAID 1, as well as multiple-level RAID involving RAID 1 (RAID 01 or RAID 10).

Striping: Striping is a technique of fragmenting the huge file (or collection of files) into indivisual Pieces (Stripes) of standard size (stripesize) and then storing the each stripes parallelly to all the Physical drives connected in RAID array.
For example, if we need to read a large file, instead of pulling it all from a single hard disk, it is much faster to chop it up into pieces, store some of the pieces on each of the drives in an array, and then use all the disks to read back the file when needed.
Striping can be done at the byte level, or in blocks. Byte-level striping means that the file is broken into "byte-sized pieces" The first byte of the file is sent to the first drive, then the second to the second drive, and so on.
Sometimes byte-level striping is done as a sector of 512 bytes. Block-level striping (group of Bytes) means that each file is split into blocks of a certain size and those are distributed to the various drives. The size of the blocks used is also called the stripe size (or block size, or several other names).
RAID 0 uses block-level striping without parity; RAID 3 and RAID 7 use byte-level striping with parity; and RAID 4, RAID 5 and RAID 6 use block-level striping with parity.
RAID 2 Uses Bit-level striping with ECC pattern but RAID2 is no more implemented anywhere because of disadvantages associated with it.

Parity: Parity technique is used as alternative technique for Mirroring because of high overhead cost disadvantage.
the term "parity" before, used in the context of system memory error detection; in fact, the parity used in RAID is very similar in concept to parity RAM.
The principle behind parity is simple: take "N" pieces of data, and from them, compute an extra piece of data. Take the "N+1" pieces of data and store them on "N+1" drives. If you lose any one of the "N+1" pieces of data, you can recreate it from the "N" that remain, regardless of which piece is lost. Parity protection is used with striping,
and the "N" pieces of data are typically the blocks or bytes distributed (Striped) across the drives in the array. The parity information can either be stored on a separate, dedicated drive, or be mixed with the data across all the drives in the array.
The parity calculation is typically performed using a logical operation called "exclusive OR" or "XOR". As you may know, the "OR" logical operator is "true" (1) if either of its operands is true, and false (0) if neither is true. The exclusive OR operator is "true" if and only if one of its operands is true; it differs from "OR" in that if both operands are true, "XOR" is false.

Concatenation or Spanning: Spanning (meaning 'Merge' drives) is a technique that allows to only group all the capacity of the multiple drives in an array. In this configuration disks storage space will be placed sequential where the Server operating system sees just one huge disk. Unfortunately, there are no other benefits except capacity with the spanning solution.
This mode is sometimes called JBOD, or "Just a Bunch Of Disks". Spanning is RAID controller (Hardware) specific implimentation and not specific to RAID implementation.