Changing raid 0+1 to raid 5

[Ali]

Hi Ajc01,

Are you looking for best fault tolerance and data safety..?

Raid 1 (2 drives) is much better implementation than Raid 5 in terms of fault tolerance and performance only draw back is you have only 50% usable space against total capacity of logical drive.
Note : sometime even if logical drive is failed for some reason you can connect this drive to some other machine and access the hard drive to see if you can extract the data but this is not possible in any other raid implementation.


Raid 1+0 (4 drives) even better infact the best raid implementation for fault tolerance and performance. again draw back is only usable space.
I should tell you that raid 1+0 (min 4 disks) on HP Smart array controller works like miracle.... it works on the fundamental of load balancing, no performance degradation even if 1 or 2 hard drives failure. the best part of this implementation is excellent data protection. if you have more than 4 drives (equal no of pairs) you will be amazed with the performance and kind of data protection.

Now I must explain Raid 6. When you are looking for more usable space in a bigger logical drive + a better fault tolerance, Raid 6 is definately a better choice.. drawback: performance and write panalties.

However, choosing the raid level is totally dependant on your environment, kind of application that you want to run, role of server, space, size, cost, fault tolerance etc. etc.. decides which raid level is the best choice for your environment.

Hope I am clear.

Cheers!
Aftab

[ajc01]

Thanks for the fast reply. The case is that it is an excisting situation with 2 logical drives on 2 arryas containing 2 drives on each array in raid 1+0. So i think if i convert each array to raid 5, I improve the data safety with 30% :) and i try to improve the write performance.

[Michael A. McKenney]

Either way, you lose two drives it will fail. Do you have a spare set up?

RAID 0+1 is four dirves. You don't have two RAID 0+1 arrays, only two logical partitions.

RAID 5 adds parity so you will slow writes.

[ajc01]

This is really weird... i'm getting confused..

I do have 2 logical drives. It says logical drive is on hdd 1+2 and logical drive 2 is on drive 3+4.

So it looks like there are 2 raid 1 arrays right ?
What is the best to do now ?

add 2 spare's ore convert it al to 2 raid 5 arrays ???

[Ali]

Hi Ajc01,

I already explained this scenario earlier... check the previous response.

Share the ADU report so that we can check the actual configuration and advice you the best option.

thanks,
aftab

[GrandSlam]

RAID 5 (3+ HDDs)
RAID 1+0 (4+ and pairs of HDDs)


Without Drive addition to existing RAID, it is possible for RAID 1+0 logical drive to convert to RAID 5. (Provided that your RAID adapter support RAID Migration, it means BBWC is need for SmartArray)

If RAID 5 to RAID 1+0, you need add more drive (also satisfy even totalt number of drive for RAID 1+0 requirement)


RAID 1+0 claims N drive for N/2 drive data space (N>1)
RAID 5 claims N drive for N-1 drive data space (N>3)

For N = 4 drives,
RAID 5 has 3 effective drive spaces
RAID 1+0 has 2 effective drive spaces

So, existing RAID 1+0 to RAID 5 will increase 1 effective drive space. But you need RAID level migration.

However, if RAID 5 to RAID 1+0, because original RAID 5 spacing > RAID 1+0 spacing, to keep the spacing, 2 additional drives needed for RAID expansion then you can migrate it.

(Don't forget RAID expansion / migration only allow original size addition but not reduction)

[gregersenj]

Well ajc. There's no really easy answer to that.

As Aftab write, an ADU report would make it easier to give you exact answer.
I hate the ADU report, I do prefer screen shots from the ACU.

The Smart Array controller (SA) got some greate advanced features, if you use the ACU for configuration.

What you need to understand, is the terms Array and logical drive, when we discuss the SA.

Array. Is a groupe of disks, that work together. And it hold 1 or more logical disks.

A logical drive, reside on an array, and it define the size of the disk you want to present to your host, and it define wich RAID level you want use, and wich disks it reside on.

You can create multible logical drives (LUN). on an Array, they don't have to be the same size or RAId level.

Possible RAID levels:
0, 1+0, 5 and 6.
Note a 1+0 using 2 disks is a RAID 1.

When a SA scans the disks during boot, it lists how many logical drives it find.

There's 2 ways to configure the SA.
1. ORCA = Utility reside on the SA ROM, and is invoked by pressing F8 during boot.
It does not give the posibilty to create multible LUN's on an Array, or to deside the size of the LUN.
> 1 logical drive per Array, using all disk space in the Array for the LUN.

2. The ACU.
The Acu can do the advanced stuff. And it work on-line.

In your case.
You could have 1 Array holding 2 LUN's.
Could be 2 x RAID 1 using disks. These will still be called 1+0.
Or you could have 2 x RAID 1+0, both using all 4 disks.
Or 2 Array's holding 1 RAID 1 LUN's each.

1 Array with 2 x RAID 1 = Add 1 more disk.
1 Array with 2 x RAID 1+0 = migrate without more disks.
2 Arrays with 1 RAID 1 eache = 2 more disks

[Ali]

Hi Ajc01,

You can not migrate existing raid volumes to Raid 5 without adding an additional drive.

This is not Raid 1+0 .... You have two Seperate logical drives with Raid 1 (2 hdd each) in the same array.

HP Array Configuration Utility does not list Raid 1 as a seperate option. it shows raid 1+0 only. If you select two drives for your logical volume it will create Raid 1 only.

Please Note : Array Expansion will play a vital role if you have just 1 Array (e.g. Array A) and 2 seperate logical drives within. Possibily you need to just add one drive to migrate both the raid 1 to raid 5.

Let me explain Array expansion a little bit..

Array is group of physical Hard drives. You can create multiple logical drives within the same group (Array). depending on the no of hard drives in a group, you will get different raid levels while creating logical drive.

There are two ways to create mulitiple logical drive with in the same group.

1. Select all the hard drives and create logical drive. at the time of creation it will give you an option to choose size of the logical drive based on which you can create another logical drive with the remaining space.

2. Select the no of hard drives and create a logical drive. select second set/remaining hard drives to create another logical drive.

So understand this.. In an Array, data is distributed across the drive during expansion. e.g when you add 1 hard drive in existing array which has raid 1 volume.. raid 1 data will be distributed across 3 drives that's the reason it will prompt you that raid 1 does not meet the minimum hard drive criteria and ask you whether you want to migrate to raid 5 which is possible with 3 hard drives.

Hope you are getting this.

So I need to understand your actual raid setup. Please share the ADU/ACU report/screenshot of logical and physical view so that I can check your actual configuration and advice you the best possible option available.

Hope you understand this.

thanks
Aftab