topic Re: Array &logical drive question - in MSA Storage

Array &logical drive question -

Haggisnneeps2 — Fri, 30 May 2008 12:02:34 GMT

I can create an array in an MSA30 with 14x 300GB drives but i have to also create logical drives. I create 2 logical drives of 2TB each but it splits them into array A and array B. Now, at this point, are both my arrays spanning all 14 drives with half a drive each?(hardware spanning - i havent got to the windows bit yet)?
Or does the ACU automatically assign 7 drives per array?
Is there any way to tell which is the case? Or does the acu also automagically give the best performing configuration?

Re: Array &logical drive question -

Uwe Zessin — Fri, 30 May 2008 17:21:08 GMT

Hm, that does not sound right.

A (SmartArray disk drive) array defines which physical disk drives belong to the group. One or more logical drives fit into a disk drive array.

If you have arrays A and B, then one array and all logical drives within that array span 7 physical disk drives and the other array spans the remaining physical disk drives.

Re: Array &logical drive question -

Haggisnneeps2 — Mon, 02 Jun 2008 07:22:32 GMT

Thats what i was beginning to suspect. Will the behaviour be the same in an MSA1000 with 2x MSA30s attached to it? In a previous post we had figured out that the best performance i could get from my MSA1000 would be to create an array across all 42 drives and then split into 2TB chunks so that each 2TB chunk would be part of a 42 drive array - giving me 42 drives worth of performance per logical drive
This would seem not to be the case then? Not only is the logical drive size limited to 2TB but the array is also limited. This, then, begs the question - what is the ACU doing when it allows you to create and array using all 42 drives and then divides that up into 2 TB luns / drives. Shouldnt there be an error at the point you try to create an array bigger than 2TB?

Re: Array &logical drive question -

Uwe Zessin — Mon, 02 Jun 2008 07:56:20 GMT

I don't know if the MSA can deal with an array which is that large. On the other hand, I've seen a customer advisory which says that multiple logical disks in an array _can_ result in performance loss.

And the great thing is - I've just checked and the advisory is still present:
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c00622089

Re: Array &logical drive question -

Haggisnneeps2 — Mon, 02 Jun 2008 08:24:15 GMT

Thanks for this but i don't think this will apply to my particular situation here....If i created 2x 1TB drives across 7 disks then yes i would expect performance to reduce since each physical drive is now effectively halved with each half being in a different array.4x 0.5TB drives ould be even worse etc

My problem is that i can't get the benefit of all 42 drives unless i'm willing to waste or throw away 5 sixths of my available storage. So now i need to experiment and figure out which is the lesser of two evils - 42 drives in an array with each drive being a member of 6 different logical drives, versus 6x arrays of 7 drives. My money is on the latter but HP recommend for 1.5TB data in millions of small files and folders that i shold be using a 60 drive array. This is quite obviously impossible to do with current limitations (unless i'm missing something)

Re: Array &logical drive question -

Herman Sugeng_1 — Mon, 16 Jun 2008 10:56:19 GMT

Hallo,
I do not sure what you up to but I think you have to choose first what is important for your application:
1. "performance" than choose an Array with RAID1+0, bare in mind allocate pairs from different enclosures.
2. Volumes than choose an Array with RAID 5, bare in mind do not allocate more than 14 disk in an array. Not advisable for transaction log of database or exchange.
The more disks in array the more performance you get.
Best regards, Herman