Hi all,
i'm a little confused over RAID.
- Data protection of Hard Drive.
Do a complete backup on a regular basis. RAID (Redundant Array
of Inexpensive Disks) - two or more drives used in combination.
- Disk mirroring
- Disk striping.
*edit*
the definition i got for disk striping from my lecture was
"dividing files into pieces and putting each piece in other
drives"
not very clear to me.
*/edit*
Can someone explain what does RAID do as well as disk mirroring
and disk striping?
Thanks
RAID is a collection of various methods to use multiple drives
like they were one single unit, whether to stripe, mirror, or a
combination.
Disk mirroring, or RAID 1, allows for protection over a disk
failure. It takes 2 drives, and data is written exactly the same
way in both drives. Basically, Drive 1 and Drive 2 share the same
contents, so should 1 drive fail, you have an exact backup in the
other drive.
Disk Striping, or RAID 0 (More like AID 0, there's nothing
redundant about this), takes 2 drives, and combines them as if they
were one big unit. It writes different sections of data into the
different drives. Take a data file for instance. It is broken up
into 6 parts, A,B,C,D,E and F, by the RAID controller. Then you
have 2 drives in (R)AID 0, D1 and D2. The controller writes A,C and
E to D1 and B,D and F to D2. So, when you are reading the file
again, the controller can read A and B simultaneously, the C and D,
the E and F.(R)AID 0 increases the capacity and speed of the array,
but also the risk. Should D1 fail in the array, all data is lost
because without parts A, C or E stored in D1, the file cannot be
read because it is incomplete.
There is also RAID0+1, and RAID10 (or 1+0). They both require 4
drives. It basically takes 1 RAID 0 array and 1 RAID 1 array. With
0+1, 2 drives are first striped. Once the RAID 0 array has been
created, the controller uses the other 2 drives to mirror the
original RAID 0 array. 1+0 is the opposite, first mirroring, then
striping. The differences, I'm not sure, but apparently they are
different enough to make controller manufacturers list them both
out.
RAID 5 is a hybrid of 0 and 1. However, it requires 4 drives
instead of 2. Lets say you have 3 data files, A, B and C,
each split into 3 parts. A1, B1, C1 and D(P) are written to D1. A2,
B2, C(P) and D1 are written to D2. A3, B(P), C2 and D2 are written
to D3. A(P), B3, C3 and D3 are written to D4 X(P) is a
parity bit, allowing the system to rebuild data parts should 1
drive fail. How it does this, I don't know. The parity bit can also
be constructed using 3 data parts, should the drive with the parity
bit go down. The advantages over RAID 1 is that you get increased
performance over RAID 1, as well as increased capacity. RAID 1
loses half the total capacity of the array, but RAID 5 loses the
capacity of 1 disk in the array. Lets say you built a RAID 1 array
with two 2TB drives. You effective data capacity is 2TB. With RAID
5, however, using four 1TB drives, you have an effective capacity
of 3TB.
