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Re: MSA 1500 Arrays

 
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Rmitchell_1
Advisor

MSA 1500 Arrays

We have an MSA 1500cs with 2 MSA30s attached. We have decided to add the final two MSA30s. Now, lets say ArrayA has 3 drives on box 1 and 3 drives on Box two with 1 LUN RAID5. If I expand arrayA with 3 drives from box3 and 3 drives from box4, will the LUN now be spread across all four MSA30s thus spreading IO across the 4 SCSI channels or will it still stay on the initial two MSA30s it was created on? The reason I ask is because I don't want to move hard drives to the new MSA30s if I don't have to. I know it will work.....but I'd rather not take the risk.
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Jefferson Humber
Honored Contributor
Solution

Re: MSA 1500 Arrays

If you expand the array and extend the LUN then all 4 SCSI channels should be addressed, due to the fact that the LUN as an entity is split across all four enclosures.
I like a clean bowl & Never go with the zero
Rmitchell_1
Advisor

Re: MSA 1500 Arrays

But what if I don't want to expand the LUN? In my scenario I don't want to.
Jefferson Humber
Honored Contributor

Re: MSA 1500 Arrays

Let me get this right.... You want to expand the array to encompass 12 HDD across 4 enclosures, but you don't want to extend the LUN in the array (in effect keeping it on the original 6 HDD across 2 enclosures)?
I like a clean bowl & Never go with the zero
Rmitchell_1
Advisor

Re: MSA 1500 Arrays

See...thats exactly what I'm asking. But allow me to clarify. My end all goal is to get my LUN which is currently only across 2 enclosures to be across all 4. So, one option would be to turn off the SAN, move some of the drives in arrayA to the new enclosures, turn it back on...thus spreading across all 4. This will definately get me what I want, but I don't like the idea of moving drives.

So, since I was already going to add more drives to ArrayA for the purposes of creating another LUN, I was hoping that I could just add the drives to the new enclosures and I was thinking that the MSA would spread the LUN across all the disks.

So I guess the real question is "does the LUN actually get tied down to the physical disk or is it virtually spread across all of them?"
kris rombauts
Honored Contributor

Re: MSA 1500 Arrays

Rmitchel,


what you had in mind with adding disks and spreading the LUN automatically over all disks in the array is how the Virtual Arrays like VA7xxx and EVA are designed to work.

I ran a test on a SmartArray 6402 with one array made out of 3 disks on port 1 and one logical drive which takes up the full capacity of the array.
When adding one disk to the MSA30 enclosure on the second channel and expanding the array by including that disk, i can see all disks being accessed when i write to that original LUN (driver x: letter in Windows).
I waited first till the expand and parity initialization was finsihed before writing to the LUN.

So because i did not extended the LUN yet, the above shows that the array already has the LUN spread over all disks right after the array expansion was finished.


Because the MSA1500 is more like the SmartArray family i tend to believe this is also how the MSA would behave in your scenario.

If allowed, you can prove this for yourself by doing the following with your six new disks:

- install the 6 new disks, 2 in each MSA30
- create a raid 5 with 4 disks in the 2 original MSA30
- create a LUN and create a partition in the OS
- write some files to the LUN and wait till the parity initialization is finished (might take some time), you can see this from the ACU status or Windows eventlog
- expand the array with disks from the 2 new MSA30 enclosures
- when the expand is finisihed and the parity initialization also, start writing to the LUN and you will see that all disks in the test array are being accessed, this will prove what you want to know.



HTH

Kris

SAKET_5
Honored Contributor

Re: MSA 1500 Arrays

A logical drive (which you are loosely referring to as LUN - Logical Unit Number) is tied to an array on the MSAs. If you expand the array of disks from which you carve your logical drive(s) but not the logical drive itself, you wont achieve what you want to! Expand the physical disk array and then the logical drive on top of it and then the OS level logical disk will be truly served by the increased number of disks.
Rmitchell_1
Advisor

Re: MSA 1500 Arrays

First off, thank you everyone for responding to my post. I just got off the phone with HP.

According to them:

If I add the new drives to ArrayA in the new shelves, the LUN will not take advantage of the new disks. However, If I expand the existing LUN just a little, the array will recalculate..or whatever it does and will respread the LUN across all disks, thus giving me the desired results.

So, I'm gonna add the shelves at our next downtime, add the disks to the array, expand the existing LUNs by 10 meg or whatever the minimum is and after doing so I'll create the new LUNs.