ProLiant Servers (ML,DL,SL)
cancel
Showing results for 
Search instead for 
Did you mean: 

RAID configuration

rpafort
Occasional Advisor

RAID configuration

Hello,

In the old days ;-) you configured your RAID based on the (number of) disks. But now you choose whatever RAID configuration you like, and I don't understand this.

To be more precise, we have a DL360G5 with a P400i RAID controller. On the older DL's I was used to create a Array and choose a RAID level for redundancy, also depending on the available disks.

Now with this machine I can create an Array, without the option to choose a RAID level. Instead I have to choose a RAID level when I create a logical disk. And to make it more confusing I can choose any RAID level, no matter the available disks. I don't understand how to translate this to the real redundancy at the hardware level.

In my case I have 4 equal disks and I created 1 array and 2 logical drives. With this 4 disks I'm able to create one mirror and 1 RAID5 logical disk?! With only 4 disks?!

Please explain to me how this is possible?

Thank you for your response.

PS: I cannot find any documentation on this from HP.
5 REPLIES
Patrick Terlisten
Honored Contributor

Re: RAID configuration

Hello,

take a look into ORCA, the rom based raid setup utility, there you will find you "old school" setup of disks and raid levels.

An array is only a set of disks. In this set of disks you can create logical drives. These logical drives have a raid level. In the HP world is a mirror and a raid 1+0 the same. With two disks, it's a mirror, with at least 4 disks it's a raid 1+0. In ACU you will only find the notation "RAID 1+0".

For a raid 1+0 you need a even number of disks. You have four disks, so you are able to create a raid 1+0 and a raid 5. With only three disks, you won't be able to create a raid 1+0, but a raid 0 and a raid 5. With four disks and a BBWC module you are able to create also a RAID ADG (RAID 6, RAID 5DP, a RAID 5 with two parity blocks).

Independent of your raid level: The Smart Array controller will distribute the blocks on the hard disks in the right order. It makes no difference if your data lies on a whole disks in a raid array, or just using a part of a disk, sharing it with other blocks.

Take a look into the ACU User Guide. There you will find lots of informations.

Best regards,
Patrick
Best regards,
Patrick
rpafort
Occasional Advisor

Re: RAID configuration

Hello Patrick,

Thank you for your reply.

I read the ACU User Guide (again), and together with your explanation this is what I understand from it;

With my setup of 4 physical disks forming 1 array containing 2 logical drives, from which 1 logical drive is a RAID 1+0 and 1 logical drive is a RAID 5, the array controller will just spread the data over all 4 disks. Correct?

If so;

1. How does this effect performance? Because you choose a RAID level for redundancy and performance. And in this case the performance gain of a RAID10 is effected by the RAID5 logical drive. In short if I would like to prevent this I need to setup 2 arrays. Correct?

2. In this case a disk failure will result a degration of both logical drives. Correct? Again the solution here is to create 2 arrays. Correct?

So in conclusion you can say that if you want an "old school" RAID level with corresponding redundancy and performance, you need to setup an array for each wanted RAID level. Correct?
Patrick Terlisten
Honored Contributor

Re: RAID configuration

Hello,

--
1. How does this effect performance? Because you choose a RAID level for redundancy and performance. And in this case the performance gain of a RAID10 is effected by the RAID5 logical drive. In short if I would like to prevent this I need to setup 2 arrays. Correct?
--

Yes and no. Surely you can build up two arrays with two drives, but with such an array, you can't create a logical drive with a raid 5. The benefit of such a configuration: More IOPS for each logical drive, the load is distributed over all four disks, and not only two disks.

--
2. In this case a disk failure will result a degration of both logical drives. Correct? Again the solution here is to create 2 arrays. Correct?
--

That's right. But remember: Two disks = no raid 5. Two disks = fewer IOPS.

Best regards,
Patrick
Best regards,
Patrick
rpafort
Occasional Advisor

Re: RAID configuration

Patrick, thank you for your responses. It's all clear to me now.
rpafort
Occasional Advisor

Re: RAID configuration

The responses are clear.