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Add disk to a raid 5 array

TJ-Zer0 used Ask the Experts™
hi can same budy tell me if its posible to add a disk to a raid 5 array of 3 disks? i got 3 36 gigs on a win2k server the controler its a smart array 5i a want to add a 4th disk to get more sotarage in the same logical drive
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Hi TJ-Zer0,


HP's website tells us that the Smart Array 5i has support for "Online Capacity Expansion" and "Logical Drive Capacity Expansion" which is fairly common for SCSI based RAID controllers.


Once you plug in the new disk, run your RAID management software to add the disk to your existing array.



Normally with Smart Array5i it should be very easily possible to add a Hard Disk Drive to get more storage space. I do not know if the Smart Array5i would support hot swapping of drives in this manner. But it will surely allow the addition of the Drives.

I have done this on Compaq DL360 G2 IIS Servers with Smart Array 51 controller. The machine was installed with Win2k Server for Industrial Telephony Test purpose.

At the same time I would also suggest that you add another Higher capacity drive just make sure that you are not faced with the same predicament of needing more space sooner or later.

Hope that this helps.

Just be very careful that you do not rebuild your entire container or all your data will be lost.

Top Expert 2014

It's pretty obvious how to add a drive to the array using the ACU running under win2k, the problem you will get is that Compaq don't like dynamic disks so although the OS sees a bigger disk you have to run the windows drive management and format it and assign a new drive letter to the extra space rather than extend the volume under win2k.

Hello TJ,
As indicated from the comments above it is definitely possible.  The main thing is to considered the situation and exactly how you want to go about this.  Here is a link that outlines expanding a RAID5 array.  also, keep in mind that there are alot of support websites out there that give you exactly what your looking for.  If you do not find this link of value, let me know as I have multiple support links.  Or you can go to dogpile.com and search for solutions.  Good Luck !!

Hi, Arjun1 says to add a larger drive so as not to run out of capacity again.
I understood that an array (Raid5) uses only the capacity of the smallest drive, so that 3 x 18GB plus 1 x 36GB drive results in the array using only the first 18GB of the 4th drive.
However, can someone advise on this hypothesis:?
I have 4 x 18GB drives. (3x18=54GB storage).
I can add 4 x 18GB (7x18=126GB storage).
But when that 128GB fills up, what do I do? Throw it all out and build a new server from the Operating System up?
What about this, add 4 x 36GB instead, rebuild the array.
Then, can I remove one 18GB drive at a time, rebuilding the array, ending up with 4 x 36GB drives, using 3x18GB capacity.
Then, once there are only 36GB drives, can I tell the controller to rebuild the array using the full 36GB capacity?
So I'll have 3x36GB=108GB storage, but then room to add another 4 x 36GB drives resulting in 252GB of capacity.
Can you do this with RAID? Or am I stuck with a limit of 18GB drives or building a new array from scratch?
Please help anyone?
Top Expert 2014

There is an alternative to reformatting the drive, use diskpart.exe from the resource kit (on the windows CD) to stretch the partition.

I'll repeat the warning, Compaq don't like dynamic disks, if you have enabled dynamic disks then do not try to expand or extend the array or you may lose the data unless you have the very latest firmware.

jon, you should really ask that as another question but yes, if you have  Compaq raid controller you can replace the drives one at a time with bigger ones and then use the ACU to see the extra space.


I think we are confusing the issue here.
Yes, indeed a Raid array may only use the capacity of the smaller Drive.
But honestly I am not talking about that, I am talking about the compaq Smart array 5i.
And I am absolutely sure that what I talked about in my last post.
The following is from the Compaq-HP Website, one tiny little detail about Smart array 5i

"Drives Supported (maximum) is based on use of Compaq StorageWorks Enclosure 4300 family (14 hard disk drive enclosure).' So now if the array used is RAID5 and if there are 14 Hard Disk drives of 10 Gigabytes each how much do you get. I think this is still more than 3X36 and I have only mentioned the lowest Hard Disk yet.
The maximum total drive supported by the Smart Array 5i is 21(raised to 2). The following website has a table
of information that will make this more clearer.

The name Smart Array 5i sitself should make this crystal clear. It is an array that supports RAID 5 and so the number of drives supported are obvious.



Top Expert 2014

Unfortunately the 4300 shelf is a couple of grand.

>>...  21(raised to 2).
that 2 is a footnote, 21 to the power 2 is one heck of a pile of disks ;)


Ya got me there Oww !  esteemed E-Expert.

Thanks a million for catching that.

Even then, 21 is still lotsa Hard Disk Drives.

Also, for non believers

RAID-5. This type includes a rotating parity array, thus addressing the write limitation in RAID-4. Thus,

all read and write operations can be overlapped. RAID-5 stores parity information but not redundant data

(but parity information can be used to reconstruct data).

RAID-5 requires at least three and usually five

disks for the array. It's best for multi-user systems in which performance is not critical or which do

few write operations.

After adding 3 disk to raid5 of hp proliant. We lost data when expanding volume with diskpart. We are try to recover!
Any suggestion?
Karthikeyan GanesanSoftware Engineer

I have IBM server ,i already configured RAID5 with three hard drive i need to expand the my stroage ,how can add two more disk with RAID5 ,PLZ tell how can i add two new dive with RAID5