cancel
Showing results for 
Search instead for 
Did you mean: 

Disk Array

Ash_4
Advisor

Disk Array

Hi to all members,
Kindly explain the following for me pl.
1. Suppose i want to configure one RAID5 set having 5 disk each of 9Gb then how much space
user will get for use and how much space we will loss.

2. Suppose i want to configure one RAID5 set having 10 disk each of 9Gb then how much space
user will get for use and how much space we will loss. Is there any fix formula to calculate the usable space and loss space.

3. I am having autoraid which consist of 12*18Gb disk, how much space user will get to use out of it.

Kindly suggest if any document explaing above is available on the net.

Thanks in adv.
:-)
9 REPLIES
Vincent Farrugia
Honored Contributor

Re: Disk Array

Hello,

9Gb * 5 disks = 32Gb with no hot spare
24Gb with hot spare

9Gb * 10 disks = 70Gb with no hot spare
62Gb with hot spare

18Gb * 12 disks = 174Gb with no hot spare
158Gb with hot spare.

There used to be a website to calculate usable capacities, but now it's gone. I found these on the PIG for AutoRAID (Peripheral Information Guide).

HTH,
Vince
Tape Drives RULE!!!

Re: Disk Array

Hi Ash,

I have a 12 x 18Gb disks in the 1 of the systems I have here at work.

This is from the arraydsp -a output

--- Disk space usage --------------------
Total physical = 208397 MB *
Allocated to LUNs = 158500 MB *
Used as Active Hot spare = 17366 MB *
Used by non-included disks = 0 MB *
Used for Redundancy = 32313 MB *
Unallocated (avail for LUNs) = 218 MB *
-----------------------------------------

Cheers
Darren
Can you imagine life without beer?
Bill McNAMARA_1
Honored Contributor

Re: Disk Array

The following links you to a utility that will calculate this for you..

http://www.hp.com/essd/model12H_autoraid_tool.html

Click on start right down on the bottom.

However, remoember the autoraid is auto. you can't say what the current capacity is for sure.. it depends on the auto migration of raid levels.

You can say for sure that maximum capacity is 10% of your total storage capacity is in R1/0 at a minimum. ie when your array is full 90% R5 10% R1/0.

Later,
Bill
It works for me (tm)
Helen French
Honored Contributor

Re: Disk Array

Hi Ash:

1) Yes, there is a common formula for calculating the disk space available in RAID 5:

Capacity in GB = (drive size) x (num drives) x (RAID factor of 0.8) / (ratio of GB to bytes = 1.024)

For your questions:

Q1 = 9 x 5 x 0.8 / 1.024 = 35.15625
Q2 = 9 x 10 x 0.8 / 1.024 = 70.3125
Q3 = 18 x 12 x 0.8 / 1.024 = 168.75

This is theory ! As you are using *AUTO* RAID, this may vary slightly; as AUTORAID puts data to RAID 5 and RAID 1 levels intermitently !

HTH,
Shiju
Life is a promise, fulfill it!
Ash_4
Advisor

Re: Disk Array

Thanks for the info. Shiju.
By the way is there any document available on the net explaining the above.

Where you get the above formula to calculate user space.
Helen French
Honored Contributor

Re: Disk Array

Hi Ash:

Again, this formula was from a book about RAID and it was almost right in all my experiences. However, nobody ever given a specific *fixed* formula for calculating the disk space for all RAID-5 arrays! It again depends on the number of disks, the disk array manufacturer (HP, IBM, Sun etc), the type of controller and the disk array logic.

For eg: most of the IBM RAID-5 arrays claims a total disk space of N-1. ie. If you have 10 disks, they offers a total disk space of 9 disk capacity without hotspare.

Check this site, this says you will get a total capacity of (N-1/N) x disk capacity:

http://www.amsstorage.com/html/raid_overview.html

This formula may be right in the case of 3 disks, but differs in case of 10 disks !

The best approach will be to find out from the disk array vendor.

HTH,
Shiju


Life is a promise, fulfill it!
Ash_4
Advisor

Re: Disk Array

hi shiju,
Is there any doc. for Nike Module 20 Array
explaining above.

thanks.
Helen French
Honored Contributor

Re: Disk Array

Hi Ash:

Again, check this document for a description about the Model 20 disk arrays:

http://www.hp.com/cposupport/information_storage/support_doc/lpg75004.html

Eventhough, it doesn't say anything about the total available capacity, in my experience you will get 80% of the total disk space available.

HTH,
Shiju
Life is a promise, fulfill it!
Sanjay_6
Honored Contributor