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Welcome to lucidEDU!  Here you'll find educational information on various data storage related topics. It is our hope that this lucidEDU will become your in-hand resource for enhancing your knowledge base and skills.

RAID 5 // Level 5 RAID // RAID Level 5

Posted on 12:32 am | 0 comments

RAID 5 / Level 5 RAID / RAID Level 5 The use of dedicated ECC / parity drives in RAID levels 1 through 4 limits each of these architectures to a single write transaction at a time, and thus they are poor choices for multitasking or transaction processing systems. RAID 5 attempts to eliminate this problem. In RAID 5, an entire transfer block is placed on a single drive, but there are no dedicated data or parity drives. Rather, the ECC blocks are distributed, as shown in the diagram below, so that each drive in the array contains a combination...

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RAID 4 // Level 4 RAID // RAID Level 4

Posted on 12:43 am | 0 comments

RAID 4 / Level 4 RAID / RAID Level 4 We said that the two primary disadvantages of the RAID 3 architecture were the large (and/or inconsistent) transfer block sizes and the inability to perform multiple simultaneous I/O transactions. Both of these problems result from the fact that a single transfer block of data is interleaved across all of the data drives. In RAID 4, we place the entire first transfer block on the first data drive, the second transfer block on the second data drive, and so forth. Diagram below shows this scheme for 4 drives....

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RAID 3 // Level 3 RAID // RAID Level 3

Posted on 9:15 pm | 0 comments

RAID 3 / Level 3 RAID / RAID Level 3 A Level 3 RAID architecture assumes that each disk drive in the array can detect and report errors. Therefore, the RAID architecture needs only be concerned with maintaining the redundant data necessary to correct the error. In RAID 3, we have two or more data disks and one ECC/parity disk. Data is interleaved across all of the data drives, so that the first byte is on the first drive, the second byte is on the second drive, and so on: If we have ‘n’ data drives, the ‘n’+ 1st byte is...

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RAID 2 // Level 2 RAID // RAID Level 2

Posted on 5:47 am | 0 comments

Level 2 RAID / RAID 2 / RAID Level 2 RAID 2 tries to get around the 50% disk overhead in the RAID 1. Four decades ago, R.W. Hamming in his “Error Detecting and Correcting Codes” research paper showed that if data could be organized so that an error was only likely to affect one bit in a group, then the error could be detected and corrected with significantly lower overhead. RAID 2 takes advantage of the Hamming codes to reduce disk overhead. The first disk drive contains the first bit in each data group, the second disk contains...

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RAID 1 // Level 1 RAID // RAID Level 1

Posted on 8:50 pm | 0 comments

Level 1 RAID / RAID 1 / RAID Level 1 A level 1 RAID is often called “mirrored disks” , “duplexed disks”, or “shadowed disks”. For each disk in the system, a duplicate disk is maintained with an exact copy of the information. Data redundancy is obvious as every byte is duplicated. Computing the performance impact is more difficult. With an optimized filesystem driver or controller, RAID 1 reads can be faster than a single drive. If we allow both drives containing the duplicate data to begin seeking together and then...

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What is a RAID System?

Posted on 5:26 am | 0 comments

What is a RAID System? The Berkeley papers do not provide a concise definition of the term RAID. Instead, they propose RAID schemes as an inexpensive method for obtaining significant increases in I/O bandwidth, and then provide an implied definition of RAID by an example of the architectures. Unfortunately, not all RAID architectures improve bandwidth. Therefore, we propose the following definition which incorporates the models presented here and that also embodies the manner in which RAID is used in the industry: A Redundant Array of...

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Data Storage – Historical Background

Posted on 5:23 am | 0 comments

Data Storage – Historical Background Humble Computing Beginnings In 1976, the microcomputer was just beginning to make personal computers a reality for a handful of individuals, the first “hackers”.  The premier systems of the day were built around an S-100 or STD bus, and had Intel 8080 or Motorola 6800 processors running with clock frequencies below 5 Mhz. The primary interactive I/O devices were converted teletypes or alphanumeric terminals from mini and mainframe computers. Primary secondary storage was...

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What is Cloud Storage?

Posted on 4:54 pm | 0 comments

Recently, cloud computing has become the latest buzzword in IT. But what
exactly is Cloud Storage and how can companies benefit from Cloud-based
Storage Solutions? We are attempting to answer this question while
exploring the many facets of data storage in the Cloud. Read on to
learn more about cloud computing, cloud storage technologies, and how
network attached storage servers are deployed to provide the access to
your data from anywhere.

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RAID-z // RAID z2 // RAID z3

Posted on 4:07 pm | 0 comments

RAID-Z is not actually a kind of RAID, but a higher-level software solution that implements an integrated redundancy scheme similar to RAID 5, using ZFS. RAID-Z avoids the RAID 5 “write hole” using copy-on-write: rather than overwriting data, it writes to a new location and then automatically overwrites the pointer to the old data.

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