Raid Group Expansion

Question

I need to expand a 5 disk (146GB) Raid 5 (4 x 1) set adding one disk. The questions are:

1. Will the current LUN be acessible to the host during the Raid Group expansion?

2. Can I use diskpart to expand the LUN on the host, using concatonation to allow the host immediate access to the increased size.

Host Info: 2 Windows Servers 2003 in a clustered environment.

I usually would create another raid Group and LUN then create a MetaLun, but I only need 133GB of additional space and I don't have anymore disks.

All LUNs are on a CX3-80 running Flare 3.26

Thanks,
Bing

AranH1 · Accepted Answer

1. Will the current LUN be acessible to the host
during the Raid Group expansion?

Yes, the existing LUN will be restriped across the disks in the RAID Group.

2. Can I use diskpart to expand the LUN on the host,
using concatonation to allow the host immediate
access to the increased size.

I believe you will have to wait until the restriping is complete before the additional space is available. There used to be an option to expand the LUN with the RAID Group if the existing LUN used occupied the entire RAID Group but the option is not available if you have metaLUNs.

So you will need to create a new LUN and concatenate it to the existing LUN.

dynamox · Answer

2. Can I use diskpart to expand the LUN on the host,
using concatonation to allow the host immediate
access to the increased size.

Host Info: 2 Windows Servers 2003 in a clustered
environment.

yes you can ..there are a few caveats you need to know dealing with expanding storage on ms clusters ...Aran is our cluster-master ...he can elaborate more on that

calle2 · Answer

I would think that the clustered disk resource would have to be online as I believe if you take the clustered disk resource offline you will loose access to it and therefore cannot expand it with diskpart...?

I would furthermore then do a fail-over to the second node to confirm that it accepts the new disk size but no expansion should be required.

As in all cases a backup prior to commencing the diskpart procedure would be highly recommended.

ovivier · Answer

Hi all,In MSCS environment, if you are not running a volume manager like Veritas Storage Foundation, you are using basic disks and you can use diskpart to expand the LUN:1) Increase the LUN on the CX3-802) Expand the partition with diskpart on the active node3) No expansion to be done on the passive node

RRR · Answer

Are you sure ? I remember having read somewhere that the cluster resource must be taken offline as well as the standby node. Then enlarge the LUN and bring everything up again.

RRR · Answer

Same as backing up... It never (NEVER) went wrong. But I guess it's all for safety. It's your data they're concerned about.

In a cluster I can imagine that if the 2nd node is still seeing the LUN while it's being expanded by the 1st node he could get confused....

ovivier · Answer

I have made the operation several times without taking offline the LUN. But if it is written somewhere to it is recommended, I would like to know where and why.

RRR · Answer

I'm sorry, I don't have the document at hand somewhere. You could try to search on Powerlink for 'lun expansion procedure' or something.

RRR · Answer

Everybody recommends backing up first: MS as well as EMC.
About having the cluster resource taken offline, I'm not sure. But expanding on 1 node is enough, the other node will work just fine when the other node did the expansion.

dynamox · Answer

Are you sure ? I remember having read somewhere that
the cluster resource must be taken offline as well as
the standby node. Then enlarge the LUN and bring
everything up again.

yep ..like calle said ..if you take disk resource offline in cluster, you will not be able to see it in Disk Management ..and diskpart will not be able to expand it either. The only issue i've see is where diskpart does its job on active node but when your fail the resource over to the standby node ..it does not see the new space until after it's rebooted.

RRR · Answer

it does not see the new space until after it's rebooted

That's what I meant. I think we meant the same thing but didn't say it right. So the 2nd node needs a reboot anyway: in that case you can shut it down (node = down, so offline), do the expansion and bring the 2nd node up again. We meant exactly the same thing.

AranH1 · Answer

You can perform the expansion of a disk assigned to a cluster on the active node with the passive node(s) online (sorry I am late to the conversation dynamox, pacific time and all that). The disk will show as expanded on the passive nodes(s) after it is expanded on the active node, but the disk resource will not failover successfully until the passive node(s) have been rebooted.

AranH1 · Answer

I read somewhere that you need to put the 2nd node
offline, but cannot fint the document anymore. It
might have been a Microsoft document... I don't
remember.

That might have been for an older rev of the OS? I have tested this in Windows Server 2003 clusters under i/o load and it worked very well.

dynamox · Answer

yeah ..i know ..silly time zones ...Thanks for clarification on the expansion question.

SanMan5 · Answer

I would like to say THANKS to everyone who answered. Like I said I've just added a single disk to a raid group for expansion, usually did a seperate radi set then a metalun. I guess it sort of the same idea just a bit of a different twist.

Thanks Again,
Bing

CLARiiON

Raid Group Expansion

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