How safe is our data in HDD ??

Hello All,

Greetings. Hope you all had a fantastic weekend, It was same for me though, spent sometime in watching some old hollywood movies and here am back with a handful. Welcome once again.

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Let me recollect the points from my last post :-)



We saw about servers,storages who are the leaders in the market.Then we also were seeing our data willl get stored in lot of harddisk drives in a storage.So how our data is protected incase of harddrive failures.So the answer is RAID.


RAID ( Redundant Array of Inexpensive Disks) :

In a very easy term, it is spreading of data in several disks instead of one.For explaining this a elucidation of RAID types is a must.It can implemented using a hardware or using a software.

Harware RAID:
Some of them use a hardware raid controller card to do all the RAID calculations.RAID controllers also come in the form of cards that act like a SCSI controller to the operating system but handle all of the actual drive communications themselves. In these cases, you plug the drives into the RAID controller just like you would a SCSI controller, but then you add them to the RAID controller's configuration, and the operating system never knows the difference.

Software RAID :
Software RAID implements the various RAID levels in the kernel disk (block device) code. It offers the cheapest possible solution, as expensive disk controller cards or hot-swap chassis are not required. Software RAID also works with cheaper IDE disks as well as SCSI disks. With today's fast CPUs, Software RAID performance can excel against Hardware RAID.

Types:
There are several RAID levels such as RAID1(Mirror),RAID 0(Stripe),RAID 5(parity),RAID 6(Distributed Parity) and so on.Let me explain some of this types.


RAID 1 :

Here data is duplicated or mirrored.That is data is mirrored one to one.So minimum we need two drives.Lets take a example with two hard drives.If a write happens say "A"on one harddisk drive it will be written on second drive also.Like this if we use 4 hard drives, we end up in using only 2 as remaining 2 are mirrored.Even if a hard disk fails the data can be recovered from its mirror.When a read happens it can read data from any of the drives from mirror.Since RAID-1 requires doubling the number of disk drives to store the data, people tend to think of RAID-1 as the most expensive type of RAID.


RAID 0 :

Data is striped on to the harddrives.Its like a paint brush.No mirroring or no redundancy.Only advantage here is its really fast. A RAID 0 array requires a minimum of two drives. A RAID 0 configuration can be applied to a single drive provided that the RAID controller is hardware and not software (i.e. OS-based arrays) and allows for such configuration.As per our classic example of two drives,if one drive fails we will lose data.

RAID 5 :
So RAID 1 is expensive and RAID 0 has no data safety.So how can this be addressed??The answer is RAID 5.
Here data is spreaded across all drives and XOR calculation of data is calculated in a distributed way.So the parity information is on all drives.It requires minimum 3 hard disks.It is inexpensive and safe too.

In my next post i will discuss about what is data center,and the career paths that you all can look into...

Cheers,
SabariGirish