Autoraid 12H LUN configuration

[Alma Eaton]

I will be installing two dual-controller Autoraids on my HP9000-K210 running HP-UX v10.20 in the near future. Each Autoraid will contain six 18GB disk drives and I will be enabling Hot Spare capability on each. I am in the process of trying to figure out to optimally define LUNS on each of the controllers. I know you can only have 8 LUNs per Autoraid and the more LUNs you have, the better the performance. I need to allow for future growth (disk additions) but still optimize performance. Do I simply define 4 LUNs for the 6 disks on each Autoraid, leaving 4 LUNs for future growth? I am unclear how to figure out how to optimally configure my Autoraid with regards to LUN definition (followed by volume groups, etc.) We will be using the Autoraids for Oracle database files. Thanks for your help!

[Andreas Voss]

Hi,

the main thing to consider is to leave enough space free (not assigned to LUN's) in the AutoRAID to give the AutoRAID the chance having as much as possible data in RAID 0/1.
Think 4 LUN's can be made but look at vg creation time for the order of the devices files added to vg. Toggle the alternate links to have 'I/O balancing' between the different vg's.
There are several threads for this, do a SERACH with 'autoraid' on the forums.

Regards

[Bob Inglis]

Autoraid Performance vs. Expandability

AutoRaid Performance considerations:
Rule #1: The more drives the better the performance.
Rule #2: Leave approximately 10% of the total physical capacity unallocated.
Rule #3: Use LVM striping and stripe across the AutoRaid controllers.

AutoRaid Expandability considerations:
Rule #1: Only 8 LUNs are supported by HP-UX (0 through 7).
Rule #2: LUNs cannot be changed, only deleted and recreated. (Requiring a reload)
Rule #3: Larger drives will probably be available in the future. (36Gig drives are available today)

Let?s look at your configuration:
6 X 18.2Gig drives with Active Spare Enabled = 67.9Gig usable, less 10% or about 61GIG on each array that we want to divide into LUNs.

If you added 6 more 18.2 Gig drives to each AutoRaid the usable capacity of each would be 166.4Gig (more than double). If you added 6 more 36Gig drives the capacity would be about 197Gig (almost triple).

I consider a 6-drive AutoRaid an ECONOMY configuration. An 8-drive configuration performs approximately 88% faster, and a 10-drive configuration performs approximately 98% faster than the 6-drive configuration. If performance is more important than Economy, you should add two more drives to each AutoRaid right now.

Your statement that more LUNs = better performance is NOT TRUE. There is one consideration though, when deciding how many LUNs to create. A LUN can only be accessed by a single controller at any given time. So, if you created one big LUN of all the available capacity you would only be able to use one controller at a time. With a dual controller Array I would think two LUNs would be the minimum you would want to create.

LVM striping is the best way to use both AutoRaid controllers simultaneously. With out striping, LVM fills up the physical volumes (LUNs) sequentially so even if you created a Volume Group of more than one physical volume (LUN), it would only use one controller until the first physical Volume was full. LVM striping requires at least 3 Physical Volumes (LUNs). So, if you only had one AutoRaid you would want to divide it into 3 or 4 equal size LUNs. With 2 AutoRaids, you would want to stripe across physical volumes (LUNs) on both AutoRaids so you would be using all 4 controllers simultaneously. Thus 2 LUNs on each AutoRaid would be sufficient.

The next concern is how many Volume Groups do you need? As LVM striping requires at least 3 Physical Volumes (LUNs), each Volume Group would require at least 3 LUNs.
So, for your Dual AutoRaid configuration;
One Volume Group = 4 LUNs, two on each AutoRaid
Two Volume Groups = 6 to 8 LUNs, 3 or 4 on each AutoRaid
Three Volume Groups = 9 to 12 LUNs, 4 to 6 on each AutoRaid
Four Volume Groups = 12 to 16 LUNs, 6 to 8 on each AutoRaid
Five Volume Groups = 15 to 16 LUNs, 7 or 8 on each AutoRaid (max)
Six or more Volume Groups = BUY ANOTHER AUTORAID
Etc.