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Multiple Logical Units with RAID 5

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Chris Moxon
Occasional Visitor

Multiple Logical Units with RAID 5


We have a HP Proliant ML350 G6 Server, with HP Smart Array P410i controller and is currently setup with 3x1TB drives with RAID 5 to give us 1.8TB of usuable storage in 1 Logical Unit. This was setup my our IS department, using whatever default seetings the ACU gave.

Now ( please bare in mind that I'm not a networky person - so all this is pretty new to me !! ) we have VM ESXi 4.1 installed on the server and as ESXI can only cope with LUNs less than 2TB everything at the moment is hunk-dory; but we actually have a spare 1TB drive that we would like to utilise on this server.

Now the question - If I add this 1TB drive to the RAID 5 configuration - it creates 1 logical unit that is 2.7 TB in size, which is too much for ESXi. So is it possible to add this new drive with the existing 3 drives, using RAID 5 but to have 2 LUNS created, so each LUN will be less than 2TB and thus ESXI will be happy ?

If this is possible - how would I go about this ? Also would this require loosing all the data that is currently on the drives ? It's not a great shame if the data is lost, as we have only just started using the server.

Thanks in advance.

Patrick Terlisten
Honored Contributor

Re: Multiple Logical Units with RAID 5

Hello Chris,

you have one array with three disks and a logical drive with a RAID 5 and ~1,8 TB. If you add the 1 TB disk to the array, nothing will happen. But you have to create a second logical drive! You must not expand the existing logical drive.

Best regards,
Chris Moxon
Occasional Visitor

Re: Multiple Logical Units with RAID 5

Hi Patrick,

Thanks for the reply ... if I add the drive and create a new logical drive ( I assume I do this via the ACU ? ) does that mean I can add it so that it is still "covered" by the RAID 5 setup ? or do I have to add it as a seperate disk/lun and thus ( I'm guessing here ) RAID 0, and thus meaning that it has not fault tollerance ?


Mark Wibaux
Trusted Contributor

Re: Multiple Logical Units with RAID 5

When you are in the ACU you will have 2 parts defined.
The first is most likely called "ArraryA" and if you switch to physical view it will consist of your 3 HDDs. Within ArrayA you should have a Logical Drive. You can have multiple Logical Drives within a single Array.

So in your case you will need to add the new disk to the existing array. Once this process is completed you should see the Array with the Logical Drive listed and then an amount of "Unused Space".
At this point you can then create a new Logical Drive within this unused space which will be within the 2TB limitation.
Clarete Riana
Valued Contributor

Re: Multiple Logical Units with RAID 5

Hi Chris,

Yes you can create 2 LUNS with the four 1TB drives that you have.

There are two options. One is without loosing the data that you currently have in the first logical unit. Steps to follow:

- Add the fourth drive.
- Expand the first logical unit using ACU. Allow the exapnsion to complete.( Make sure the controller allows expansion)
- Now the first logical unit will span across four disks and there will be unused space that you can see after the expansion is complete.
- Create the second logical unit using the unused space on the array of four drives.

By doing this, the size of your first logigal unit will remain same as it is now ( 1.8TB), but it will span across four drives. Second RAID 5 logical unit can be created using the same space. Note that you cannot reduce the size of the first logical unit from the curent 1.8TB.

The second option you have is to delete the first unit. (you will loose data if you do this). But advantage is you can recreate the two new RAID 5 logical units on the four drives with whatever size you want.

Let me know if you need any further clarifications.

Chris Moxon
Occasional Visitor

Re: Multiple Logical Units with RAID 5

Many thanks to everyone who replied with suggested solutions ... I was rather excited ( though that feeling didn't last long ) with Mark's reponse, because it seemed to make sense and was easy ... but I still could not work out how to do it within the ACU !

I was just about to reply last week, saying that I didn't have any options to do what he suggested ... but then eventually realised that the reason why I had not got the options was due to our licence for the SmartStart software. In order to get the options we needed, we would have to stump up £250 for a new licence ... so in the end I did the second option that Clarette suggested and basically wiped everyting down and created two 1.4TB LUNS from scratch !!