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Basic RAID tutorial and/or info

Posted on 2005-05-03
Medium Priority
Last Modified: 2008-01-09
Hi all - I'm considering at a RAID1 or 0+1 for my workstation, and while I know the basics I'd like more information on this topic. Could someone either give me a solid overview of the basic workings of RAID (like what happens when a disk dies, for example), as well as the the pros/cons of doing something like this? Links to online resources would be fine as well.

My mobo (ASUS P4P800 Deluxe) supports 0, 1 and 0+1 for the IDE RAID, and 0 or 1 for the SATA RAID. My goal is to minimize the downtime and rebuild associated with disk failure, especially bootdisk failure.
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Expert Comment

by:Duncan Meyers
ID: 13922199
This is pretty good: http://www.acnc.com/04_00.html

There is also a good primer at www.arstechnica.com

RAID 1 is probably your best bet - excellent redundancy and good performance.

Assisted Solution

Budrick1000 earned 400 total points
ID: 13923183
The tutorial posted by meyersd has some good info.

I have the same motherboard, I think it comes with Promise software that has some capabilities like emailing you when something goes wrong with a RAID array.  

I have used all sorts of different RAID arrays...mostly for performance though.

RAID 0 - I liked them for performance, but never stored anything critical. This probably isn't what you are looking for based on your post. The more drives in the array, the faster but make sure they are the exact same type of drive with same capacity and buffer sizes. If not its not worth it.

RAID 1 - Came in handy when a disk died. The RAID controller on the motherboard will detect a broken array. You can either keep it like that (but not be able to use the disk), or disassociate the disk from the array so it can be used on its own. The controller doesn't care what order the drives are plugged in as. It does care if you try to add a blank drive to a broken array. I never tried it but I dont think it will let you do it, you have to disassociate it first and start over again after backing up your data.
RAID 1 arrays drop performance. I only store stuff that I dont use much on them or critical things. RAID 1 will not protect you from corrupted data because it writes the same thing to two different drives at the same time. If you use it on a booting disk make sure you back stuff up onto something else.

RAID 0 + 1 - I think this requires 4 drives, never did one but its good for performance and redundancy.

If you want to be able to rebuild data you are going to need RAID 5. It requires minimum 3 drives.

An alternative to a RAID array via a hard drive controller would be Dynamic Disks in Windows XP. This can be found under disk management in the computer management snapin of MMC.
You can do all sorts of arrays with it.

Hope that info helps

LVL 30

Accepted Solution

Duncan Meyers earned 1200 total points
ID: 13923796
Just a couple of notes:

RAID 0 is not RAID!! It has no redundancy and so is best left to the brave. A quick browse through this topic area will find plenty of questions along the lines of "My RAID 0 array broke and my data is gone :-("

RAID 1 and RAID 10 - excellent redundancy, RAID 10 has excellent performance for both read and write operations. Typically RAID 1 has good performance for reads (ie better than single disc), and no better than single-disc performance for writes.

RAID 5 has excellent redundancy and very good read performance but very poor write performance due to teh RAID 5 write penalty (that is; for every write operation the controller must: 1. Read original parity. 2. Read original data. 3. XOR parity and data to obtain a partial product then XOR this partial product to get the new parity. 4. Write out the new parity. 5. Write out the new data. Sl-o-o-o-o-o-w... Write caching goes some way to helping here depending on a number of factors.

It should be noted that none of the RAID levels guard against file system corruption at the OS level. If the OS writes out bad data, then that is what is written to disk. The RAID 5 parity scheme does provide a level of confidence that the data coming off the RAID array is exactly as written, but it doesn't guarantee that the data is "good" as far as the OS is concerned. Garbage in = Garbage out.
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Assisted Solution

by:Gary Gordon
Gary Gordon earned 400 total points
ID: 13924769
Inexpensive Hardware Based RAID1 solution:

RAID1 involves two identical harddisks that contain exactly the same information.  When 1 disk goes down, the machine is rebooted out of the remaining disk after a breif warning that you need to fix or replace the failed disk.  Some server operating systems like Windows 2000 have RAID configuration options, but I like using a cheap PCI RAID1 Card instead like the Adaptec 1200A.

You install the card like any other PCI card, then you install the RAID management program, and then turn the PC off.  Disconnect the hard disk IDE cable from the mainboard and connect it to the 1st IDE connector on the card.  Connect your second identical harddisk to the 2nd ID connector and then boot up.

You then reboot and use the software to create an array.  Disk 1 is copied to disk 2 and thats all.  In this situation it is allways best to have two identical hard disks when you begin and it is better to buy larger disks so that you have room to grow into them.  Here is an example on Ebay:


You can buy used Adaptec PCI RAID cards cheap off of Ebay.  
LVL 85
ID: 13924905
Thanks all ... I certainly understand more about RAID now, and your comments have helped to clear up my thinking on the subject. I'll definitely NOT be using a RAID0 array, but instead a RAID1. My primary concern is data protection, and I've come to understand that RAID1 provides me more protection against a failed disk but does NOT really protect my data (I need a ghosting or imaging prog for that, along with a solid backup prog). I've posted another question in the Hardware area regardingmy specific troubles, and I believe this is the solution I'll be using:

Promise TX2200 RAID controller
One SATA 80 GB Seagate Barracuda, one SATA 120 GB Seagate Barracuda w/ one partition for all OS, apps, data, etc
One IDE 80 GB Maxtor harddrive to hold ghost/acronis images
RAID 1 using the SATA drives
Weekly ghosting to 160 GB USB drive (or after prog installs/updates)
Daily backup using either Danz Retrospect, Iomega or Genie backup to 160 GB USB drive
LVL 30

Expert Comment

by:Duncan Meyers
ID: 13925758
Both discs should be the same size in a mirror pair. I'm not familiar with the Promise RAID controller, but you may have 40GB of wasted space on the 120GB disc. The controller may not allow you to partition the unused 40GB of space (you'll be limited to 80GB mirrored).
LVL 85
ID: 13925839
Yes, I realize I'll lose the 40 GB, but I'm not overly concerned with that - I had the one 80 GB drive running for 1+ years and only used about 25 GB of it, and that was with very poor housekeeping practices <g> ... I'm promising myself that I'll do better in the future ... but you know how that goes. I'm assuming that, if I begin to run into space issues, I could swap the 80 GB for a new, matched 120GB?

Expert Comment

by:Gary Gordon
ID: 13928835
I like your 120GB drive pair idea.  Good luck with it!  Don't forget to dole out the points! : )  ggordon777
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Expert Comment

by:Duncan Meyers
ID: 13931601
> I'm assuming that, if I begin to run into space issues, I could swap the 80 GB for a new, matched 120GB?

Maybe yes, maybe no. It depends on the RAID controller. It would be far better to build the mirrored pair with a couple of 120GB discs now rather than run into grief later.  

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