HP P2000 SAS Array - Expand vs New

Posted on 2014-09-05
Last Modified: 2014-09-17
God day,

I have a potentially simple questions.

I have an HP P2000 SAS array that hold 24 sff 900GB drives.  It connects two HP Proliant DL385p servers via redundant SAS controllers per server.  We installed 12 drives to begin with and created two vdisks, one RAID5 with hot spare and one RAID10 wth hot spare.  All works perfectly.  Client has asked to populate the remaining 12 slots with new drives.  I have inserted all 12 with identical drives as the first 12.  All are AVAIL.  But before I pull the trigger on the configuration, I am a little fuzzy on what will happen as I have had no way to test different scenarios.

*  It looks like I cannot expand a RAID10 V-disk as the P2000 seems to want only 4 drives and any number of hot spares per RAID10 V-disk, so if I need additional RAID10 space, I need to create a new V-disk.  True/false?

*  With its own hot spare, or can an existing hot spare be assigned?

*  For the RAID5 V-disk, is it best to create new V-disk or should I expand the existing V-disk?  

*  Seems to me that expanding the RAID5 will allow me to make better use of the drives since I already have the hot spare configured,  True/false?

*  I am affriad that expanding will make the system unusable until the expand has finished.  True/false?

*  Is there something I am totally missing with this array that I am not seeing?

Simple, right?

Thank you

NMJ Technology LLC
Question by:Michael Jackson
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LVL 39

Accepted Solution

Aaron Tomosky earned 250 total points
ID: 40307171
Id advise against raid 5 with that many drives, go for raid 6 to sleep well during a rebuild.
LVL 39

Assisted Solution

by:Philip Elder
Philip Elder earned 250 total points
ID: 40307186
One RAID 6 array would perform a lot better and as mentioned offer better resilience.

We had a server drop a drive in a RAID 10 array. We hot replaced it. About 3 minutes later its mirrored pair died. RAID 6 and we would have still had the server. We will never do RAID 10 again.

That being said, in our testing when it comes to 16+ spindles there is not a lot of performance to be gained with RAID 10 over RAID 6.

We would back up, shutdown, R&R the array setup, and then restore the servers. It would be a lot quicker than migrating new storage in too.
LVL 82

Expert Comment

by:David Johnson, CD, MVP
ID: 40307615
Raid 5 has outlived its lifetime.  Current Hard drives all have errors that the built in error correction does a pretty good job of repairing read errors on the fly. But once you have more than 12TB of drives in a RAID5 array you will get bitten with most drives (10^14 URE) when doing a rebuild.  Normal raid has resiliency but in a raid rebuild you don't have any resiliency.  

Most SAS (and not SAS/SATA) drives have an URE of 10^16 ..  Always remember that RAID does not equal backup.. you need another copy non raid of what you have on a raid volume always.
Where there is a drive failure pull any unbacked up data - latest documents that aren't backed up - off the RAID before replacing the failed drive.
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Assisted Solution

by:Michael Jackson
Michael Jackson earned 0 total points
ID: 40319155
I appreciate all the input about RAID5 versus RAID6.  No one actually addressed the specific questions I had about expanding the existing volumes.  But, I will probably end up creating a new volume with these last drives in a RAID 6 and not try to expand anything.

Thank you.

LVL 39

Expert Comment

by:Philip Elder
ID: 40319388
In all of the storage shelf setups we work with expanding takes _a long_ time. It is a resource intensive process not to be taken lightly.

Adding drives to the RAID 5 setup on a guestimate would take a few days per drive to migrate into the array. The RAID 10 would probably be longer given the array gets expanded by two drive pairs at the minimum.

Sorry, should have spoke to the specific question instead of getting all preachy. ;)

Author Comment

by:Michael Jackson
ID: 40319419
It's all good.

Turns out that doing a new RAID array with the remaining 12 drives sounds cleaner than trying to expand either the existing RAID 5 or RAID 10.  But the comments about RAID 6 versus RAID 5 did sway me.

Thanks again.

LVL 39

Expert Comment

by:Aaron Tomosky
ID: 40319904
glad to help. watch how calm you are during the next drive rebuild

Author Closing Comment

by:Michael Jackson
ID: 40327553
I had asked a questions that was more about expanding existing volumes on an array, and no one actually addressed these.  The answers were more about the RAID levels I was already using.  However, I did reconsider the situation and also decided to abandon the "expand" method and go with a new RAID6 array partially on what these people suggested.

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