RAID stands for what?

[Szech]

I was told that RAID stands for R.edundant A.rray of I.dentical D.isks. Namely, because the hard drives have to be identical sizes. But I just read the instructions on how to make the Promise 66 card do RAID (very interesting, BTW), and it said it stood for R.edundant A.rray of I.nexpensive D.isks. Who's right? The disks have to be the same size, right?

[brandon184]

RAID : Redundant Array of Independent Disks

http://www.sysopt.com/forum/wink.gif

[mgordon99]

RAID is Redundant Array of Independent Disks. I believe there are 5 RAID levels, not sure if the diskd need to be the same size, but it may be so. http://www.sysopt.com/forum/smile.gif

[KillerBug]

They need to be the same size for some modes, but some modes do not need it. And it is inexpensive disks.

[brandon184]

KillerBug - You sure?

Take a look at whatis.com.

[BBA]

KB's right, no lying, as evdenced by raid controller manuals and the jbod modes of raid.

[Wiz]

I dont think RAID was ever "standardized" name-wise. there are 5 different settings.

0-creates 1 big HDD from a few smaller ones.

1-1 HDD is an exact mirror of the other

2-uses 32 drives to create 7, very fast, and expensive

3-strpies data across multiple drives. It is seperated into bytes

4-same as above, but they are seperated into blocks

5-the best kind of RAID, error-correction data which goes across all drives, the best for hot-swapping.

correct me if i am wrong, but this is how i remember it.

[Mntsnow]

Here is a great little site that will answer you questions on all the different raid levels http://www.sysopt.com/forum/smile.gif
http://www.acnc.com/raid.html

Mntsnow

[hd581]

I think there's a RAID-6 either in development or available that allows 2 drives to fail and the array can still recover.

[Szech]

Cool, thanks everyone. As for having the ability to have two drives fail, I think that would be too much space lost (or apportioned rather). I'm already a little hesitant to drop half the available space of additional hard drives.

[CONTRiC]

The "I" in RAID has been changed many times and many people say it differently. The older meaning of RAID has always been Redundant Array of Inexpensive Disks.

[Kido]

I am MCSE and in the all of the books i have read it is "Inexpensive"

[hd581]

We have tread this ground before in a previous post. (http://www.sysopt.com/forum/Forum1/HTML/005110.html)

To sum it up, it was originally coined by its creators in a paper called “A Case for Redundant Arrays of Inexpensive Disks (RAID)”.

[CONTRiC]

The different RAID levels

RAID-0:
RAID Level 0 is not redundant, hence does not truly fit the "RAID" acronym. In level 0, data is split across drives, resulting in higher data throughput. Since no redundant information is stored, performance is very good, but the failure of any disk in the array results in data loss. This level is commonly referred to as striping.

RAID-1:
RAID Level 1 provides redundancy by writing all data to two or more drives. The performance of a level 1 array tends to be faster on reads and slower on writes compared to a single drive, but if either drive fails, no data is lost. This is a good entry-level redundant system, since only two drives are required; however, since one drive is used to store a duplicate of the data, the cost per megabyte is high. This level is commonly referred to as mirroring.

RAID-2:
RAID Level 2, which uses Hamming error correction codes, is intended for use with drives which do not have built-in error detection. All SCSI drives support built-in error detection, so this level is of little use when using SCSI drives.

RAID-3:
RAID Level 3 stripes data at a byte level across several drives, with parity stored on one drive. It is otherwise similar to level 4. Byte-level striping requires hardware support for efficient use.

RAID-4:
RAID Level 4 stripes data at a block level across several drives, with parity stored on one drive. The parity information allows recovery from the failure of any single drive. The performance of a level 4 array is very good for reads (the same as level 0). Writes, however, require that parity data be updated each time. This slows small random writes, in particular, though large writes or sequential writes are fairly fast. Because only one drive in the array stores redundant data, the cost per megabyte of a level 4 array can be fairly low.

RAID-5:
RAID Level 5 is similar to level 4, but distributes parity among the drives. This can speed small writes in multiprocessing systems, since the parity disk does not become a bottleneck. Because parity data must be skipped on each drive during reads, however, the performance for reads tends to be considerably lower than a level 4 array. The cost per megabyte is the same as for level 4.

Clip taken from: http://www.uni-mainz.de/~neuffer/scsi/what_is_raid.html

[Pepto]

I always thought it meant ReAlly paranoID
http://www.sysopt.com/forum/smile.gif

[CONTRiC]

With the amount of ecommerce transactions and business clients that need to be handled 24/7, RAID is only the first step (and even then it has many short commings). RAID is only a small part of a properly designed and thought-out server. Backup's, hardware, even redundant hardware (eg: a SCSI controller for each physical drive, spare drives to take over for failed disks, hot-swap options, etc). Then there are UPS considerations and a whole wack load of other things to think about http://www.sysopt.com/forum/smile.gif

Just remember your contingency plan http://www.sysopt.com/forum/smile.gif

[hd581]

Bah, most of us don't have our computers operating 24/7. RAID offers a cheap solution for speed and fault tolerance, the opportunity to save data safely and w/ much less worry than if it was on a single drive. These are things the average Joe can afford and appreciate.

BTW, when I say operating, I don't mean "on". I also don't mean "on and running something like All-Advantage Browse Hack". http://www.sysopt.com/forum/biggrin.gif Neither of these benefit from RAID.


[This message has been edited by hd581 (edited 04-18-2000).]