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raid5 expansion question

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Eric Gilam
Occasional Visitor

raid5 expansion question

I have a Smart Array 642 Controller that has 4 300GB discs in a RAID5 configuration. I would like to add another four discs at 300GB each, but I have some questions before I do this. If I choose to do the expansion option in the HP Array Configuration Utility, here are my questions:

1) How long will it take (or how could I calculate this)?

2) Will cause a problem if the data on the current four drives is accessed by users during the process?

3) However unlikely, but what happens if the process fails?

4) Anything else I should be aware of when doing something like this?

Just want to make sure before I actually do this.

Thanks.
6 REPLIES
Jefferson Humber
Honored Contributor
Solution

Re: raid5 expansion question

Hi Eric,

1. HP quote approx 15mins per Gb, but in reality I have found this to be quicker. It depends on your configuration, and Expand priority setting on your controller.

2. You can do this as an online operation, but performance will suffer.

3. Not good, make sure you have a good backup before starting.

4. Personally, I would ensure my firmware was up to date on my SA controller before I started, and made sure I had a good backup.

Hope this helps,

Jeff
I like a clean bowl & Never go with the zero
Eric Gilam
Occasional Visitor

Re: raid5 expansion question

Thank you for the information. Is it problematic or possible to change the expand priority as I see fit? For instance, low during the day, and high during the night.

I have a great backup, the problem is that I cannot have down time, people work late hours with this data, and the data is always changing. I want this process to go as quickly as possible.

Thanks again.
kris rombauts
Honored Contributor

Re: raid5 expansion question

Eric,

you're getting very close to the maximum logical drive size (2 TerraByte) with those 8 * 300 GByte in raid5, you will probably be just below the limit.

An alternative would be to assign one new disk as a hotspare and add the 3 remaining new disks to the existing array, resulting in 7 * 300 GB raid5 array.
Or just create a new 4 * 300 GByte array as your second array but that might not fit your capacity needs and application.


I have a 4 * 300 GB array in raid 5 and that gives me 858293 MB as raw logical drive in ACU and 838 Mbytes in Windows disk management. So since the raid5 overhead is already taken into acocunt here, adding 4 * 300 GB will add approx 4 * 286097 MB= 1144388 Mbytes, making the total raw logical disk in ACU equal to 858293+1144388 = 2002681 MB which is just below the max 2 TByte.

Unless someone can point to some table/matrix that shows this is possible with just one logical drive, i'd add 3 disk first to expand and see where you get and then decide to add the 4-th disk or not and use it as hotspare.

Pls note that rebuild times in case of a disk failure in such large arrays are very long and impact performance since your data is needed and changing thru the whole day.
Check again if a second array isn't a possible solution for you.

HTH

Kris


Eric Gilam
Occasional Visitor

Re: raid5 expansion question

Creating a second array was not an option. I've already started the expansion process with 8x300GB RAID5. Like you said, it is just barely below the 2TB limit. I'm at 2% in 24 hours. In retrospect, I think that going to the three drive expansion with the 4th as a hot spare is what I should have done. Two questions I have now are:

1) Can I cancel or reverse this process? I think I'd like to go for the 3 drives expansion with a hot spare.

2) If it is not possible to cancel, I'd like to get this expansion done as quickly as possible. Is it possible to bump up the expansion priority during the expansion process? I've got some nice windows to do some heavy crunching on the drives this weekend.

Any advice is appreciated.
kris rombauts
Honored Contributor

Re: raid5 expansion question

Eric,

no, their is no way back in this expand process and later on their is also no way to remove a drive to go from 8 to 7 i.e.
This is the kind of status message you will see when looking now in the ACU :

//////
The current array controller is performing capacity expansion, extension, or migration on array B.

Additional expansions, extensions, and migrations are not allowed on this controller until this process is complete. Also, configuration changes to any other array that is waiting for expansion or rebuild are not possible until this process completes. If unused space exists, additional logical drives can be created. Otherwise, most configuration changes are not allowed until this process is complete.
/////


The only thing you can do to speed up the expansion is to let the server alone (no user workload ....) and make sure the controller properties are set to HIGH for the Expand priority in ACU. You can change this online and just have to save the new setting if you make a change.

Maybe also skip your virusscan and backup job if their is one scheduled in the next days) as this will add additional delay due to the disk access those jobs will be doing.


Because the BBWC (battery backed write cache) on the controller is also disabled during an expansion, the performance of your system might be slower now for any new read/write operations of your users.
Once the expansion is done, it will be re-enabled. In your system.evt log you will now see these kind of messages :

Event Type: Warning
Event Source: Storage Agents
Event Category: Events
Event ID: 1200
Date: 3/16/2007
Time: 1:49:24 PM
User: N/A
Computer: xxxxx
Description: Drive Array Logical Drive Status Change. Logical drive number 2 on the array controller has a new status of 12.

(Logical Drive status values: 1=other, 2=ok, 3=failed, 4=unconfigured, 5=recovering, 6=readyForRebuild, 7=rebuilding, 8=wrongDrive, 9=badConnect, 10=overheating, 11=shutdown, 12=expanding, 13=notAvailable, 14=queuedForExpansion)


Event Type: Warning
Event Source: Storage Agents
Event Category: Events
Event ID: 1204
Date: 3/16/2007
Time: 1:49:24 PM
User: N/A
Computer: xxxx
Description: Drive Array Accelerator Status Change. The array accelerator board attached to the array controller has a new status of 4.
(Accelerator status values: 1=other, 2=notConfigured, 3=enabled, 4=tmpDisabled, 5=permDisabled)



Kris
Eric Gilam
Occasional Visitor

Re: raid5 expansion question

I just bumped the controller up to high priority for the weekend, and I will bump it back down during the next working week. After the expansion is complete, I will add another drive as a hot spare. Thank you for the help.