What is raid?

[fstime]

Title says it all, raid 0, raid 1? Is raid like, taking 2 HDs and combining them? I really have no clue, thanks.

 

[tweeve2002]

Basicly RAID 0 puts half the data on one drive and half the data on the other...Its a little more complicated then that but thats the basics. It can sometimes help preformance by reading and writing to both drives at the same time. With RAID 0 if one drive fails, you can loose all data on your system.

RAID 1...Places exact copys of the data on both drives. one drive is a perfect back up of the other...if one drive fails its easy to replace the failed drive and rebuild the array. RAID 1 can read data just as fast as RAID 0 because when it read, it can read off both drives at the same time. One disadvatage of RAID 1 is that it takes at least 2 drives of equal size and you only get the size of one drive.

hope this helps.

 

[fstime]

I guess raid 1 is for me, thanks.

 

[dszd0g]

FAQ: What are the different RAID levels and what are they used for?
With a few additions:

RAID 0, 1, 5, and 1+0 are 99% of the RAID one sees.

There is both RAID 0+1 and RAID 1+0, the difference in what order the RAID mirroring and striping is done. In RAID 0+1 one creates the striped arrays first, and then does the mirroring. When 1 drive fails in 1 array, that array is disabled. If a drive fails in the other array the entire array is lost. In RAID 1+0 one mirrors each drive first, and then create an array. As long as the 2 drives in each mirror does not fail, the array is maintained. Some vendors use RAID 0+1 and 1+0 interchangably, but it is good to make sure one uses 1+0 if one desires stripping and mirroring.

Highpoint is now calling RAID 1, RAID 1.5 because they interleave read requests between the two disks for performance, which some of their competitors were not doing. This is already done by a lot of SCSI RAID 1 controllers, but nothing distinguished between RAID 1 that had this feature and RAID 1 that did not. However, 1.5 is a misnomer as it has nothing to do with RAID 5.

Another feature is spare drives or "hot spares." Most server RAID arrays make use of spare drives so that when a drive fails the array automatically uses the spare drive to rebuild the failed drive and notifies the system administrator that a drive failed. On highly fault tolerant systems the amount of time it takes to rebuild a failed drive is one measure of the reliability as that can be a vulnerable time period.

Other high availability options include: hot swap, the ability to swap drives, power supplies, or fans while the array is operating, and redundant power supplies and fans.

There is also EMC Corporations Parity RAID or "RAID S" which is similar to RAID 4, except that each disk contains a volume rather than splitting a volume across all the non-parity disks.

There is also Double parity RAID 5. While RAID-6 just makes a copy of the parity information, Double parity RAID 5 keeps two sets of parity information one for a volume across the disks and one for all the volumes on a single disk.

Some people refer to RAID 0 as rAID 0 to emphasize that it is not really a RAID as it is not redundant.

Another term one may come across is JBOD (Just a Bunch of Disks), while not RAID, a lot of RAID controllers support JBOD and it would be helpful to explain what it means.

FAQ: Hard drive interfaces and standards