How to calculate the capacity of a RAID system

[M.KANAGARAJ]

Hi ,

How will you calculate the capacity of a RAID 5 system ?. i am having a Proliant DL380 G3 server with SMART 5i controller,which is configured with 3 X 72.8 GB hotplug scsi HDDs in RAID5. I am getting only 135 GB of space out of it & i want to add 2 or 3 more HDDs .
What is the procedure to calculate the capacity of the RAID 5 logical drive after the upgradation.? ..like how much i will get for storage and how much will be used for Parity information.. etc.

TO expand an existing Logical drive
What are the options available to me ?

Is it possible to increase the size of an existing array / logical drive by adding more hard disk drives.( without creating a new logical drive )If so How?..

Thanks & Regards

M.Kanagaraj

[SAKET_5 · Accepted solution]

Hi Kanagarj,

Generally to calculate the effective or useable capacity of a RAID 5 set/LUN is calculated using the formula (n-1)/n, where "n" is the number of drives in your RAID 5 set. The rest goes to store parity information.Note that in your case with 3*72GB drives, if you use the above formula you will get an effective figure or roughly around 145GB. This doesnt quite match up with your 135GB. This is explained by the fact that the label at the front of the disk is generally the marketing figure based on the assumption that 1GB=1000MB instead of 1GB=1024MB.

To expand a logical drive, you must first expand the logical array which is what you plan to do. Then depending on the OS, i will just assume you are running Windows, if the disk is basic, you can use Microsoft's utility called "Diskpart" to extend basic disk partitions on the fly or if you are using dynamic disk, you can just right click on the volume and extend it.

Yes, it is possible to increase the size of an existing array on SA5i controller. Use ACU to expand your existing array. Straightforward but could be time consuming. Some HP documents indicate it takes 15 minutes per GB for array expansion.

Let me know if you need to know any further.

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Enjoy!

[M.KANAGARAJ]

Hi SAKET,

Nice answer & thanks for it . If i have doubts on this , i will come back to you.

Thanks for your valuable reply ,

Best Regards

M.Kanagaraj

[SAKET_5]

Hi Kanagaraj,

pleased to know the answer was of help to you.

yes, feel free to post any more queries and I am sure the forum will come forward to help you as much as possible.

regards,
Saket.

[M.KANAGARAJ]

Hi saket,

Thanks .

Regards

M.Kanagaraj