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Please Explain RAID on an HD
- Thread starter NeoGreen
- Start date
Johnthephoneguy
Technical User
Raid is used to create a large HD using multiple smaller ones, or to increase the speed by writing to more than 1 drive at once. It is also used for data backup.
You would take two 50GB drives and raid them to create one 100GB drive. Then the system will write to it much faster than them being 2 drives.
JohnThePhoneGuy
"If I can't fix it, it's not broke!
You would take two 50GB drives and raid them to create one 100GB drive. Then the system will write to it much faster than them being 2 drives.
JohnThePhoneGuy
"If I can't fix it, it's not broke!
LWComputingMVP
IS-IT--Management
johnthephoneguy is only vaguely correct, at best.
I would suggest you review the Wikipedia RAID entry:
That said, RAID is a *R*edundant *A*rray of *I*nexpensive *D*isks. There are several different kinds of RAID - the three most common are RAID 0 (which is NOT really a RAID), RAID 1 (sometimes called "mirroring") and RAID 5.
RAID 0 can make things faster as it combines two or more drives so they appear to be one larger drive - it's faster because there are more heads ("eyes") looking over the data when you ask for it. If any one of the disks in a RAID 0 fails, you lose EVERYTHING ON ALL DISKS. For this reason, I do not recommend it EXCEPT when you are doing video editing and things like that - then you would use a RAID 0 disk as a workspace only, NEVER storing data there that didn't have a backup elsewhere.
RAID 1 uses TWO drives (typically of identical sizes) and writes the same information to both drives. So if you have TWO 100GB hard drives, Windows will only see ONE drive. But if either drive fails, the other drive has all your data and keeps running as if nothing happened.
RAID 5 uses 3 or more disks and combines them similar to a RAID 0, except that one disk worth of space is used for Parity. This parity allows for ANY of the 3 or more disks in the RAID set to fail and yet the data is STILL there and accessible, though the performance will decrease as the system must now recreate the lost disk's data from parity when you try to access it. Other than speed issues, this is transparent. If a RAID 5 loses MORE than one disk at any given time, then ALL data is lost on all disks (just like a RAID 0).
RAID is NOT a backup. RAID cannot protect you from losing data due to fire, accidental deletion, or file system corruption.
I would suggest you review the Wikipedia RAID entry:
That said, RAID is a *R*edundant *A*rray of *I*nexpensive *D*isks. There are several different kinds of RAID - the three most common are RAID 0 (which is NOT really a RAID), RAID 1 (sometimes called "mirroring") and RAID 5.
RAID 0 can make things faster as it combines two or more drives so they appear to be one larger drive - it's faster because there are more heads ("eyes") looking over the data when you ask for it. If any one of the disks in a RAID 0 fails, you lose EVERYTHING ON ALL DISKS. For this reason, I do not recommend it EXCEPT when you are doing video editing and things like that - then you would use a RAID 0 disk as a workspace only, NEVER storing data there that didn't have a backup elsewhere.
RAID 1 uses TWO drives (typically of identical sizes) and writes the same information to both drives. So if you have TWO 100GB hard drives, Windows will only see ONE drive. But if either drive fails, the other drive has all your data and keeps running as if nothing happened.
RAID 5 uses 3 or more disks and combines them similar to a RAID 0, except that one disk worth of space is used for Parity. This parity allows for ANY of the 3 or more disks in the RAID set to fail and yet the data is STILL there and accessible, though the performance will decrease as the system must now recreate the lost disk's data from parity when you try to access it. Other than speed issues, this is transparent. If a RAID 5 loses MORE than one disk at any given time, then ALL data is lost on all disks (just like a RAID 0).
RAID is NOT a backup. RAID cannot protect you from losing data due to fire, accidental deletion, or file system corruption.
The best and most comprehensive RAID guide I have found is here:
...although Wiki is excellent also. These not only explain how RAID works, but also interesting information about the less-popular RAID levels.
Thanks lwcomputing for pointing out that redundancy is not a substitute for backup...EVER
Tony
...although Wiki is excellent also. These not only explain how RAID works, but also interesting information about the less-popular RAID levels.
Thanks lwcomputing for pointing out that redundancy is not a substitute for backup...EVER
Tony
Johnthephoneguy
Technical User
If you do not consider Raid 1 a backup of your data then whats the point of it?
No it is not a backup in the sense of an offsite storage, but if your primary drives fail you do have a copy of everything.
I was being very basic in my first response on purpose.
JohnThePhoneGuy
"If I can't fix it, it's not broke!
No it is not a backup in the sense of an offsite storage, but if your primary drives fail you do have a copy of everything.
I was being very basic in my first response on purpose.
JohnThePhoneGuy
"If I can't fix it, it's not broke!
biglebowski
Technical User
RAID is not a backup it's increased resilience, by striping or mirroring the data across various disks you make it possible for a damaged disk to be replaced and rebuilt from the others.
When I was born I was so suprised I didn't talk for 18 months
When I was born I was so suprised I didn't talk for 18 months
- Moderator
- #8
See post thread602-1291745 
I thought I gave a pretty good description of raid in there.
Just my 2¢
"In order to start solving a problem, one must first identify its owner." --Me
--Greg
I thought I gave a pretty good description of raid in there.
Just my 2¢
"In order to start solving a problem, one must first identify its owner." --Me
--Greg
RAID is for fault tolerance. It protects you from the failure of a drive, and makes your system more resilient. If you lose a hard disk in a RAID array, you can continue to work without downtime and without losing any data (assuming that you're not running RAID0).
Backups are for disaster recovery and data retention. If your entire PC goes up in flames RAID does you no good, but a backup of your PC can be used to rebuild your PC, minus the data that was created/changed since the last backup. Periodic backups can also help you to recover from corrupt data, accidental deletions, etc. RAID doesn't help you at all there.
They have two completely different purposes really.
- Thread starter
- #10
LWComputingMVP
IS-IT--Management
With RARE exception, I recommend using RAID on EVERY server. Servers perform functions for your business and most businesses would lose more money from being down for a few hours or even days than it would cost to buy a second hard drive and RAID controller (Depending on exactly what kind of drives and hardware, the cost could be as little as $50-75 and as much as $1000's).
Workstations, not so important. If a workstation fails, one person is inconvenienced... if a server fails, MANY people can be inconvenienced.
Workstations, not so important. If a workstation fails, one person is inconvenienced... if a server fails, MANY people can be inconvenienced.
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