What is RAID?

JBOD! I was going to post about JBOD, but figured that this was the RAID thread, so...

Just a Bunch Of Disks. Functional, but what happens if, say, your drive that's holding all your modding pictures goes belly up?

I'll take RAID any day of the week, tyvm.

Harddrives are fairly cheap now. I bought a Western Digital Caviar SATA II harddrive for 43 bucks of newegg. Shouldn't put a big hole in your wallet to go buy one.

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Originally Posted by XcOM

i prefur JBOD!!
My old server used mirrored, i used it for stabilty and backup, mainly coz i transfur LOADS of data, Alot of the time, so i want backups, i've only had to restore the drive twice.

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Originally Posted by DrumThumper

JBOD! I was going to post about JBOD, but figured that this was the RAID thread, so...

Just a Bunch Of Disks. Functional, but what happens if, say, your drive that's holding all your modding pictures goes belly up?

I'll take RAID any day of the week, tyvm.

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I have a JBOD sitting right next to me, connected to my Octane2 that has 10 drives, software raid 0.

Oh and I pre-date most of you and when I was taking my UNIX tests several decades ago, the ONLY correct answer was; Redundant Array of Inexpensive Disks. Some electronic terminology has become out dated. Just like SCSI; Small Computer Systems Interface. Some of the systems that rely ONLY on scsi are far from small...

RAID is called inexpensive because it used cheaper formats for work.
Much, much cheaper than old big iron stuff from the 70's and 80's. I'm sure bozo could fill you in on this much better than myself.

In modern times, it's called RAID and it doesn't matter which version you prefer. What matters is that it works, and works well.

Is there a difference between jbod and a regular raid setup or is it just another way of saying raid?

I'm surprised that no one mentioned that mobo-integrated raid is almost always soft raid. It relies on the processor to do it's number crunching. If you're talking big raid 5 or 50 arrays, that's some serious processing.

Hard raid is almost always a separate card running PCI 64 bit or PCI-X.
The most common units that I know of use XOR processing. Could someone elaborate on this?

Modern raid cards come in different interface and configuration flavors. From a cheap 20 dollar 0/1/10 pata 100 PCI card to a 1000 dollar 0/1/3/5/10/50 12 port sata 2 setups.

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Originally Posted by nil8

RAID is called inexpensive because it used cheaper formats for work.
Much, much cheaper than old big iron stuff from the 70's and 80's. I'm sure bozo could fill you in on this much better than myself.

One of my first real computer jobs was fixing disk drives. 500mb drives that took 2 people to lift and measured 19" wide, 12" high, and 24-30" deep. A refurbished one cost $20k. I know, I knocked one off of a cart and could not fix it. I heard about that for the rest of the time I was there (Amoco Production in Denver). We used to replace the heads, motors logic boards and platters. It took about 3 hours and an ocilliscope to re-align it after swapping any parts. The bottom layer of the bottom plater was nothing but an alignment track. I also fixed floppy drives. Head replacement, motor replacement, calibration. It was cheaper at the time to repair the drive instead of buying a new one.

In modern times, it's called RAID and it doesn't matter which version you prefer. What matters is that it works, and works well.

Is there a difference between jbod and a regular raid setup or is it just another way of saying raid?

Typically when referring to a JBOD vs RAID enclosure, the RAID enclosure had the necessary onboard logic for RAIDing the drives, whereas the JBOD did not (although you could hook it up to an external RAID device).

I'm surprised that no one mentioned that mobo-integrated raid is almost always soft raid. It relies on the processor to do it's number crunching. If you're talking big raid 5 or 50 arrays, that's some serious processing.

Sort of but not quite. Take for instance the raid setup I mentioned at my house. It is completely transparent to the OS that there is a RAID device. The motherboard handles everything. There is however a driver that has to be loaded into windows to recognize the device (F6). None of the raid logic is done in windows, so it really is hardware raid. HOWEVER, most of the add in raid cards (the expensive ones anyway) have their own processor and memory on board to handle ALL the raid functions, taking the load off of the onboard CPU. Now I am curious if there is a performance hit on the processor to handle the raid stuff. I know there logically has to be, but how much? I have been itching to do some raid testing with both sata and scsi drives to determine thew speed boost, once I am done with the next cluster installment and have the Modders Challenge underway I will have to test this. I have access to a machine that can handle the 64 bit raid cards and have a low end and a high end card here at work.

Hard raid is almost always a separate card running PCI 64 bit or PCI-X.
The most common units that I know of use XOR processing. Could someone elaborate on this?

You got me on that one....

Modern raid cards come in different interface and configuration flavors. From a cheap 20 dollar 0/1/10 pata 100 PCI card to a 1000 dollar 0/1/3/5/10/50 12 port sata 2 setups.

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...you forgot the $2k SAS raid card... ;)

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Originally Posted by nil8

I'm surprised that no one mentioned that mobo-integrated raid is almost always soft raid. It relies on the processor to do it's number crunching. If you're talking big raid 5 or 50 arrays, that's some serious processing.

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Like AB said, If there is hardware present to handle the RAID logic, then it would be hardware RAID. I mean if you really come down to it ALL RAID is software. Since there isn't a mechanical device separating the bits to each drive, its software that does the work. The difference is where the software is being executed from. If there is a dedicated device that controls the RAID logic its hardware, if it is controlled by the OS or some program that is loaded into the OS then its Software RAID.

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Originally Posted by nil8

Hard raid is almost always a separate card running PCI 64 bit or PCI-X.

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Those are most common today, but RAID controllers were also available in 16 bit ISA/EISA slots and of course 16 and 32 bit PCI slots as well. RAID technology was first developed in 1987 as software and later in '93 the development of Hardware RAID devices began.

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Originally Posted by nil8

The most common units that I know of use XOR processing. Could someone elaborate on this?

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XOR processing is basically what I explained in the first post about parity. I was trying to keep it really simple. Paritly actually uses a subset of binary artithmatic called Bitwise Operation. So where I said:

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Originally Posted by OvRiDe

0+0=1
0+1=0
1+0=0
1+1=1

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Really its

0 XOR 0 = 1
0 XOR 1 = 0
1 XOR 0 = 0
1 XOR 1 = 1

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Originally Posted by Airbozo

HOWEVER, most of the add in raid cards (the expensive ones anyway) have their own processor and memory on board to handle ALL the raid functions, taking the load off of the onboard CPU. Now I am curious if there is a performance hit on the processor to handle the raid stuff. I know there logically has to be, but how much? I have been itching to do some raid testing with both sata and scsi drives to determine thew speed boost, once I am done with the next cluster installment and have the Modders Challenge underway I will have to test this.

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In the post below,the link to THG has some perfomance charts toward the end of the article, that shows the performance of several RAID controllers as compared to the Software RAID used by Windows XP. I would be curious to see actual charts of the CPU usage during write and read operations, as well as during the rebuild process.

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Originally Posted by OvRiDe

Here is an article from THG where they explore RAID 5 in Windows XP. I found the last page with the performance charts quite interesting. It demonstrates the performance difference between Hardware RAID setups and Software RAID.

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If you get a chance to do that testing, I would love to see the results.

Great stuff here man.

-Dave

i like JBOD on my system maily becuase its my main machine, I have no use for fancy setups, No need for backups, and its fast enough for what i do, theres no Vital data stored on it, ON CD-Images (BACKUPS OF COURSE) of which the orgionals are in a wallet, to prevent damage, Random Downloads and my OS, all on 3 HDD's,

Its strange, theres setup in JBOD eventhough there on a "Promise Ultra100 TX2" raid card, Wonderful cards, and i did see a peformace JUMP from onboard IDE to the raid card. My server holds all my documents, music and other stuff, everything thats important and i can't be arsed to store on my machine.

And to answer your question, what is one failos in JBOD, simple, use a disk recovery (Provided its still detectoed by bios) and recover, and replace the drive.


Never had to do that on my machine!