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RAID 5 Expansion

Paul Gloser
Occasional Visitor

RAID 5 Expansion

ML350 G4 with 6 36.4GB drives setup as RAID5 - single logial drive, two partitions. System partition space ok, but need to add capacity on data partition. What is procedure to replace drives? (not physical install - what is required and/or most efficient process for on-line expansion? i.e. replace one drive at a time? would replacing specific drives facilitate online array rebuild/expansion? how long might rebuild process take? would it be quicker to take it offline and pull disk image back from local NAS device? Any inputs, URLS to docs, other suggestions appreciated.
8 REPLIES
SABManoj
Advisor

Re: RAID 5 Expansion

Hi Paul, I guess you need to be more clear on the query. To add storage space to a LUN then follow these steps.
1) From Array Configuration Utility, Extend the Array by adding new installed drives
2) Expand the logical Volume. Here is the ACU guide

http://h10032.www1.hp.com/ctg/Manual/c00709035.pdf

3) Once OS is able to see the space added, you can use diskpart at OS level to extend the volume.
http://support.microsoft.com/kb/325590

Also, RAID Rebuild/expansion/migration takes around 15 min per GB of data.

I hope it helps

Cheers!
Paul Gloser
Occasional Visitor

Re: RAID 5 Expansion

Thanks for the response. Am looking for most expeditious approach to expand data partition capacity. Was hoping to swap drives and rebuild online; but with all 6 physical drives on a single logical drive, replacing/rebuilding would take a week; and even then, am unclear whether the extra capacity be available to an existing partition (or as new partition). i.e. array rebuild will limit use of the 72GB drives to 36GB so long as there is a 36GB drive in the array; but does that limitation go away after the last 36GB drive has been replaced?

Sounding like new array config with disk image restores is best solution. was hoping to avoid that much downtime (it's SBS 2003 running Exchange etc.)
Bhavnish Kamboj (BK)
Trusted Contributor

Re: RAID 5 Expansion

Hi Paul,

In this case if you replace your drives with higher capacity, you will not be able to use extra space because this raid is not virtual, its physical.

So only two options for you:

1. If you have empty bays available then put higher capacity drives, create new array then logical drives and move the data from this array to newly created one. But I think you already have 6 drives populated so not possible in your environment.

2. Now you are left with one option, take backup of existing data and restore it to new array of higher capacity drives.


Note: The solution which you are talking about above of replacing one drive at a time is not feasible here but feasible in HP EVA Storage as it works on virtual raid.


BK
wobbe
Respected Contributor

Re: RAID 5 Expansion

A week to rebuild 6x 36.4 GB drives?
Sounds a bit extreme if you ask me. Are the disks heavily utilized?
Replacing the disks one at the time, expanding the logical volume and then expanding the partition should work with the setup you have.
gregersenj
Honored Contributor

Re: RAID 5 Expansion

HP say:
Rebuild can take up to 15 min / GB.
Thtas worst case. Slow disk's, alto of them in a RIAD 5 or 6, And a busy controller.

On a ML350 G4, wit a Smart Array 641 and 3 x 36G 15RPM U320 Disk's in a RAID 5.
> 12 Minutes
The server was not highly loaded.

I would expect less than 1 hour per disk in your case.
If it is very busy, it could take longer.

In my oppinion, your choice is.
1. Extra security, and scheduled, long down time.
2. Mostly on-line. less secure.

Choise 1. Make the image. Shut down server. Remove disks. Install new disks. redeploy server.
here the security is, that if you get problems with the new installation. You can quickly revert to the old disks.
Down side is, you have got a longer down time.

Choise 2. Ensure you have got a good backup and emergency restore plan.
Replace disks 1 at the time.
Extend the logical disk, or create a new.
This is all on-line.
depending on what you want to do. You might have to take down the server for a few minutes, to extend the system/boot partition.
Depneds on OS and witch partition you need to extend.

BR
/jag
apple13140
Occasional Advisor

Re: RAID 5 Expansion

Yeah, you can check this article for reference, depend on your situation, you can find whether it is helpful:
http://www.dynamic-disk.com/resource/software-RAID-and-dynamic-disk-introduction.html
Paul Gloser
Occasional Visitor

Re: RAID 5 Expansion

Thanks to all who responded. We ended up spending a Saturday replacing all drives at once and restoring from image.

With a few similar situations in the field, we may yet try the online/one at a time thing; but given that this was SBS running Exchange plus a couple SQL databases, I'd expect this machine would have been on the higher end of the 12 - 15 min/GB range. A week (or a few days or whatever it may have been to install one, await rebuild, install two, rebuild...etc. thru disk 6) seemed more stressful than a 1/2 day of weekend downtime knowing we'd still have Sunday to go back if we needed to punt. ;)
Paul Gloser
Occasional Visitor

Re: RAID 5 Expansion

see above