Blockchain

What is Hashing?

Hashing is simply passing some data through a formula that produces a result, called a hash. That hash is usually a string of characters and the hashes generated by a formula are always the same length, regardless of how much data you feed into it. For example, the MD5 formula always produces 32 character-long hashes. Regardless of whether you feed in the entire text of MOBY DICK or just the letter C, you’ll always get 32 characters back.

Hashing is One-Way

Hashing works in one direction only – for a given piece of data, you’ll always get the same hash BUT you can’t turn a hash back into its original data. If you need to go in two directions, you need encrypting, rather than hashing.

With encrypting you pass some data through an encryption formula and get a result that looks something like a hash, but with the biggest difference being that you can take the encrypted result, run it through a decryption formula and get your original data back.

Remember, hashing is different – you can’t get your original data back simply by running a formula on your hash (a bit about how to hack these, though, in a moment).

To salt a hash, simply append a known value to the string before you hash it. For example, if before it’s stored in a database every password is salted with the string ‘dog’, it will likely not be found in online databases. So, password salted with dog (i.e. passworddog) and then run through the md5 calculator becomes 854007583be4c246efc2ee58bf3060e6.

Reference:

 https://www.edureka.co/blog/interview-questions/blockchain-interview-questions/

https://dataspace.com/big-data-applications/what-does-it-mean-to-hash-data/

System Analyst - 1

 

RAID

RAID stands for Redundant Array of Inexpensive Disks. That means that RAID is a way of logically putting multiple disks together into a single array. 

RAID 0 (Striping)

RAID 0 is taking any number of disks and merging them into one large volume. This will greatly increase speeds, as you're reading and writing from multiple disks at a time.

RAID 1 (Mirroring)

A pair of identical disks identically mirror/copy the data equally across the drives in the array. The point of RAID 1 is primarily for redundancy. If you completely lose a drive, you can still stay up and running off the additional drive.

RAID 5/6 (Striping + Distributed Parity)

-RAID 5 requires the use of at least 3 drives (RAID 6 requires at least 4 drives). 

-It takes the idea of RAID 0, and strips data across multiple drives to increase performance. But, it also adds the aspect of redundancy by distributing parity information across the disks. 

-With RAID 5 you can lose one disk, and with RAID 6 you can lose two disks, and still maintain your operations and data.

-RAID 5 and RAID 6 are often good options for standard web servers, file servers, and other general purpose systems where most of the transactions are reads, and get you a good value for your money. This is because you only need to purchase one additional drive for RAID 5 (or two additional drives for RAID 6) to add speed and redundancy.

-RAID 5 or RAID 6 is not the best choice for a heavy write environment, such as a database server, as it will likely hurt your overall performance. 

RAID 10 (Mirroring + Striping)

RAID 10 requires at least 4 drives and is a combination of RAID 1 (mirroring) and RAID 0 (striping). This will get you both increased speed and redundancy. This is often the recommended RAID level if you're looking for speed, but still need redundancy. In a four-drive configuration, two mirrored drives hold half of the striped data and another two mirror the other half of the data. This means you can lose any single drive, and then possibly even a 2nd drive, without losing any data. Just like RAID 1, you'll only have the capacity of half the drives, but you will see improved read and write performance. You will also have the fast rebuild time of RAID 1.