Configuring RAID for the first time.... 1

[johnpau80]

Hi All,

I am planning to configure RAID for the first time.

I am getting a DELL 2900 power edge server without any OS
with 5 disks.

1 & 2 for OS (with RAID 1 )

3,4, & 5 for DATA ( with RAID 5 )

How easy is it to configure this for a first time user ?

Any other things I need to consider ?

 

[LawnBoy]

It's no big deal. Read the RAID documentation for that server and you should have no problems.

 

[wahnula]

First, format all the drives. I like to write zeroes to all drives before creating any array, using mfgr utility. You will need (2) RAID controllers. Most RAID arrays need to be configured in sysBIOS before loading an OS. I've never built a Dell array, but here's my procedure for typical onboard or RAID card install:

1) Buring BIOS boot, look for the key combo to press to enter RAID BIOS for the controller you want to use for each array; there will hopefully be (2)
2) Create the OS RAID 1 array first; reboot.
3) Create the RAID 5 array. Reboot
4) On the Dell disk there should be a "make disk" or "drivers" folder. You will need to create a floppy with the RAID drivers for Windows, not sure about Linux & others.
5) During OS load (boot) keep pressing F6 to let Windows know you've got a driver floppy;
6) At the appropriate prompt, insert the floppy and "Yes" your way through the driver install. You will probably need to do this twice.
7) Choose the smaller array (RAID 1) for the OS install.
8) After oS is installed, go to Disk Management and in itialize the RAID 5 array for use as a drive;
9) When installing your OS, make sure you assign the program files to the RAID 1 array and the data files to the RAID 5 array.

Best of luck!

Tony

 

[kmcferrin]

I doubt that you will need two RAID controllers. Most commercial servers will allow you to build multiple arrays from a single controller. The servers (at least HPs) typically come with some sort of installation software CD that you boot from that allows you to configure the server (including making RAID arrays), select the OS, and the launch the OS install. Usually when you use this process it will automatically handle the mass storage drivers.

Also, instead of making two separate arrays you could make a single large array and split it into two partitions. Add another hard disk and go with RAID 10 for higher performance all around.

 

[johnpau80]

Thanks guys for your replies.

Yeah usually the DELL servers come with some installations
CD ,which we need to load and prepare the server to install
any OS. And I guess I had seen in my current servers where
it gives me an option of configuring RAID during this initial
setup.

So if I were to configure RAID do I just need the select
the disks and set them up RAID 1(1st & 2nd disk) and RAID 5
(3,4 & 5th disks). Is it user friendly and can we do
it just with mouse clicks ?


---Thanks
SAM

 

[gbaughma]

Wow.... Personally, I would do all 5 drives as Raid5, and partition OS and data partitions instead.

I *HATE* Raid 1. I had a drive corrupt, and in the process of corrupting, my Raid-1 controller dutifully mirrored all the corruption to the other drive. Yuck.

Here's the skinny.

Physical Drives join together into a Container.
A container contains one or more LOGICAL drives.
LOGICAL drives can be partitioned just like regular drives.

To figure out your storage for RAID 5, use the following simple method.

If you have 5 drives, and they're all going to be RAID 5 (and they're all the same size, obviously... they have to be)... add up the storage capacity of 4 drives.

For example, if you have 5 100-GB drives, you'll get about 400GB of storage.

It's always the (number of drives - 1) x Capacity. Simple.



Just my 2¢

"In order to start solving a problem, one must first identify its owner." --Me
--Greg

http://parallel.tzo.com

 

[wahnula]

I *HATE* Raid 1. I had a drive corrupt, and in the process of corrupting, my Raid-1 controller dutifully mirrored all the corruption to the other drive. Yuck.

With all due respect, that's what backups are for. RAID 1 is not to protect data from corruption, it is to double (or more) MTBF. If your data became corrupt on a RAID 5 array would the parity data not be corrupt too? Dual arrays is a belt-and-suspenders approach but neither RAID 1, RAID 5 or RAID 10 is meant to be a replacement for regular, scheduled backups.

Tony

 

[LawnBoy]

There's a very good reason for putting the OS on RAID1 (I do it on every server). It is faster to write to RAID1 than RAID5 (RAID5 reads faster). And your swap file is written to constantly.

I don't see how RAID5 could prevent data corruption any better than RAID1...

 

[gbaughma]

Don't get me wrong. It doesn't replace my backups, which is a complete backup every single night in an 8-cartridge robotic library.

BUT... it was the drive failure that was corrupting the data, and that corrupted data was copied over.

In the event of a drive failure in RAID5, your container is still intact, although degraded.

Bottom line, I've never had data loss due to a hard drive failure in a RAID5 scenario, but I *have* had it in Raid 1.



Just my 2¢

"In order to start solving a problem, one must first identify its owner." --Me
--Greg

http://parallel.tzo.com

 

[johnpau80]

Umh.... good inputs..

As newbie quick questions:

In RAID 5 with ( 3 x 100GB ) as per gbaughma we get
a capacity of 200GB. How is data written when we fully use
200GB (is it not mirrored, if the drive crashes you said
it will recover the whole data . Where does it store the 200GB data as there is 100GB .

Trying to understand the basicas of RAID, sorry for noive Q's

 

[wahnula]

There is good info here:

http://www.pcguide.com/ref/hdd/perf/raid/levels/index.htm

It is done with what is called parity data, splitting data amongst the available drives so any one drive can go down.

Tony

 

[gbaughma]

johnpau80:

Yeah... the "basic" explaination is this.

DRIVE 1 DRIVE 2 DRIVE 3

1/2 of the data 1/2 of the data error-checking


OK... so... if I'm writing 1/2 of the data to one drive, 1/2 of the data to a second drive, and error-checking (in the form of CRC) to the third drive, I can rebuild any of the three drives if one of them fails.

It's like this:

1 + 1 = 2 (data on the three drives)
? + 1 = 2 (data on first drive is failed... but I know what was on the first drive by subtracting the second from the third)
1 + ? = 2 (data on the second drive failed... but I know what it was by subtracting the first from the third)
1 + 1 = ? (data on the third drive, error-checking drive failed... but I can rebuild it because I have all the data from the first two drives)

OK, I know this is ***EXTREMELY*** over-simplified... but you get the idea.



Just my 2¢

"In order to start solving a problem, one must first identify its owner." --Me
--Greg

http://parallel.tzo.com

 

[kmcferrin]

I agree, very oversimplified. With RAID 5 there isn't a dedicated disk for parity data, as there is with RAID 3 and 4. Instead the parity is rotated among the available disks, so that the partify for a particular data stripe may be stored on disk 1, but the next stripe will be stored on disk 2, the next one on disk 3, and so on.

Other than that, it's a pretty good explanation.

 

[gbaughma]

kmcferrin:

I *said* it was over-simplified. <LOL> *logically* what I posted works. I know that in practice, it's a much different critter.

As I was thinking about this post, I was wondering if I shouldn't have explained it with a parity bit instead.... those are easy to figure out, too, once you know how they work.

Just for those who are afraid to ask, here's a SIMPLIFIED version of how parity would work, using the same three-drive scenario.

Even or Odd parity works by making the bits either an even or odd number.

SO.....

DRIVE 1 DRIVE 2 Drive 3 (Even Parity)
0 1 1 (now it's an even number of bits)
1 1 0 (even number again)
0 0 0 (Still an even number)
1 0 1 (an even number again)

.... SO.....

? 1 1 (drive 1 must have been a 0)
0 ? 1 (drive 1 must have been a 1)
0 1 ? (parity must have been a 1)



Just my 2¢

"In order to start solving a problem, one must first identify its owner." --Me
--Greg

http://parallel.tzo.com