Expand Raid Group by adding 2 new disks

I've moved this question into the CLARiiON forum - more likely to get an answer.
Julie Gibson

The best option here is most likely to make use of MetaLUNs, and expand the existing LUNs by either Striping or Concatenation. From the question below, it sounds like the client is really concerned about LUN capacity (not how the RAID Group is constructed). MetaLUNs (and the ability to perform Striping and Concatenation) were introduced to allow the capacity of LUNs to be expanded in an efficient manner.

For information about the use of MetaLUNs, see the whitepaper "EMC CLARiiON MetaLUNs - Concepts, Operations, and Management".
It's available on Powerlink in several places, including;
Home > Products > Hardware/Platforms > CLARiiON > CLARiiON CX300 > Technical White Papers

Regards,
DGM

P.S. Disks cannot be directly added to an existing RAID 1 group - RAID 1 is not expandable beyond 2 disks. For clients who wish to implement mirrored RAID, and may later want to expand the RAID Group beyond 2 disks, RAID 1/0 should be configured (RAID 1/0 is configurable from 2 to 16 disks, in increments of 2).

Hi,
Initally, I thought we bind 2 new disks as RAID 1.Then expand the existing the RAID Group 1(RAID 5 )luns to create Metalun.If that is the case, the usable space will be 146GB as user thought they can use 2 disk space if the disks can be expand through the RAID group.

I have extract the information from the administrator Guide as shown below:

You can expand a RAID group by adding one or more disks to it.
Expanding a RAID group does not automatically increase the user
capacity of already bound LUNs. Instead, it distributes the capacity
of the LUNs equally across all the disks in the RAID group, freeing
space for additional LUNs.
If you expand a RAID group that has only one bound LUN with a
user capacity equal to the user capacity of the RAID group, you can
choose to have the user capacity of the LUN equal the user capacity
of the expanded Group. Whether you can actually use the increased
user capacity of the LUN depends on the operating system running
on the servers connected to the storage system.
Note: If the storage system supports metaLUNs, the Expand LUN with
RAID group feature is unavailable.

Pls advice.

You noted;
"Initally, I thought we bind 2 new disks as RAID 1.Then expand the existing the RAID Group 1(RAID 5 )luns to create Metalun.If that is the case, the usable space will be 146GB as user thought they can use 2 disk space if the disks can be expand through the RAID group."
--> The above is essentially an example of using MetaLUNs to expand capacity. The nuance here is that it is not really the existing RAID Group that gets expanded; what happens is the new RAID Group is used to add space to the existing LUNs. The end result will be that the existing LUNs get larger (which is what the client needs) and those LUNs get some of their usable space from the existing RAID Group, plus some more usable space from the new RAID Group.

You also quoted a section of the Admin Guide that says;
"You can expand a RAID group by adding one or more disks to it.
Expanding a RAID group does not automatically increase the user
capacity of already bound LUNs. Instead, it distributes the capacity
of the LUNs equally across all the disks in the RAID group, freeing
space for additional LUNs."
--> The above is something that cannot be done to an existing RAID 1 - a RAID Group constructed as RAID 1 cannot be expanded to more than 2 disks. However, expanding the RAID Group is not really what needs to be done for the client (the client needs the LUNs expanded, not the RAID Group). As noted in the discussion above, you are thinking of binding the 2 new drives into a RAID 1, and then using that capacity to make the existing LUNs larger. That's fine, and is an example of using MetaLUNs.

The MetaLUNs whitepaper covers general considerations and options in more detail.

Regards,
DGM

I think there may be some confusion here in the interpretation of the original note.

If I'm not mistaken the RAID1 referred to in the initial request was RAID group number 1 with is actually a RAID5(5+1) group. If this is the case, I can't see any reason not to add the two new drives to the existing RAID group. It would not increase the size of the existing LUNs, but new LUNs could be created on the additional space and added to the host.

This would be preferable to creating a new RAID1(1+1) since the usable space would be doubled.

It all depends on what you want to accomplish.

MetaLUNs didn't exist when I started working with CLARiiONs, so we use a mix of the old and new depending on the situation.

If your goal is to maximize usable space on the new drives (and performance is not a critical issue) then expanding the RAID group then adding additional LUNs to the host will let you get almost the full space out of the two drives. It just means that you need to use dynamic volumes on your windows host and create a spanned volume to increase the size of the existing drives.

Otherwise, the MetaLUN option will simplify the config on the host (at the cost of half your usable disk space).

You pick.

I have always used the Metalun option (safe, and easy). Create a another raid group bind a lun to it. Then Within the Storage Group containing the original LUN select that LUN and right click then select expand. The wizard will come up and walk you thorugh the process, I usually select concatonate rather than stripe (faster). Once that is done you will have to Run Diskpart on the host in order for it to see the new disk size.

Bing

Hi,

By adding the 2 drives via the RAID Goup---> Properites-Disk--->expand,it will distributes the capacity of the LUNs equally across all the disks in the RAID group, freeing space for additional LUNs.Initially I have 6 Luns created in the RAID Group, user required to expand disk space only on 3 luns.

Q1.I have to bind additional 3 luns from the free space after the expand and then use the expand Storage Wizard to create Metalun to increase the DiskSpace.Am I correct.

Q2.How long will it takes to expand 6XRAID 5(146GB) with 2 additional New disk as user will shutdown the system.

Q1. You are correct, once you expand the raid group you will have additional usable space in that raid group to create new luns and then use Metalun feature to expand existing luns.

Q2. It depends on how busy your array is, i just expanded a 5x268G raid group by adding one additional 268G drive ...it took 5min to expand but my raid group only had one 4G lun.

If you have a RAID 5 Raid Gourp, you can add additional disks to expand the Raid Group, but not the existing LUNs in that Raid Group. Once the new disks have completed expanding, you can now create new LUNs from the new space in the Raid Group.

The question about metaLUNs is a different question. Just creating new LUNs can be done by adding more disks to the Raid Group.

Hi,
I believe it can be done with the Existing Luns with Metalun with the newly created Luns as indicated in KnowledgeBase: emc116735

Environment: Product: CLARiiON CX-Series
Environment: EMC SW: Navisphere
Problem: Why doesn't LUN show expanded size after adding disk to RAID group?
Problem: LUN shows same size after adding a disk to RAID group?
Change: More space was needed so a disk was added to a RAID group. The LUN does not see this space.
Root Cause: Although the RAID group was expanded by adding a disk, the LUN(s) bound to the RAID group will not automatically reflect this additional space. The expanded space in the RAID group is available to bind new LUNs.
Fix: To expand a LUN in a RAID group that has been expanded by adding a disk, follow one of these procedures:
If customer environment is such that data on the LUN can be deleted, the LUN can be unbound. A new LUN can then be created with the expanded space.

OR

If the customer environment is such that data must be preserved on the LUN, new LUNs can be bound with the expanded space in the RAID group. The original LUN can be expanded with a metaLUN created to include the existing LUN and new LUN(s).

Pleas see the White paper on MetaLUNs - you do not want to create three new LUNs in the same raid group and then use these three LUNs to create a single metaLUN - the performace will be poor and affect the performance of the other LUNs in the raid group. Also see the EMC CLARiiiON Best Practice for Fibre Channel Storage - release 22 - this paper will provide a lot of good information on expnading LUNs and raid groups with an eye towards performance - use this as the first place to start.

glenk