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georgemasonFlag for United Kingdom of Great Britain and Northern Ireland asked on

How long to add 2x300GB SAS disks to RAID5 MSA2000 array?

Hi,

I need to add a couple of disks to a RAID5 vdisk on an MSA2312i. I've read that it can take a long time. The new disks are actually in a RAID1 vdisk at the moment which I'll drop and add to the RAID5 instead (currently has 4 x 300GB disks). What I'm trying to work out is:

1. How long??? Some estimates sound insane - 4 days or more??
2. Is the array accessible during this time?
3. If so, how badly is performance degraded

Thanks

G
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georgemason

8/22/2022 - Mon
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jakethecatuk

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Hossy

1. How long really depends on a number of things which include: the I/O activity on the array, the priority setting of rebuild/expansion on the controller, the speed of the disks, and the speed of the controller.
2. I presume you have the MSA2000 connected to an HP-branded controller.  HP-branded controllers will rebuild/expand an array online (meaning is will be available).
3. That depends on the priority you have configured for rebuilds/expansions on the controller.  It's a simple trade off -- performance of array versus speed of rebuild/expansion.  Since the array is online during this time, "how long" is virtually impossible to calculate.

However, the expansion can be done with both disks at the same time.  I would recommend starting this on Friday after business hours to minimize user impact which in turn gives the controller more cycles to work on the expansion versus serving user requests.  Of course, I'm presuming your low I/O points -- since you know your system better, start the process right before your normal low I/O periods.
ASKER
georgemason

Hi both,

Thanks for your comments. The array is under pretty light load so am hopeful that it shouldn't take too long. Downside is that its a 7 day week office so there are no days when the machines are completely free, although the weekend is less busy.

The disks are all 15K SAS so should be as fast as they can be, the controllers are both HP devices (shipped with the array). At the moment the "utility priority" is set to high - assume this is the rebuild priority?

Can I change the rebuild priority on the fly? Perhaps then I can start it on high priority and lower if it impacts the user experience. I will try and move some VMs off the SAN before adding the disks if only to lower the load on the storage as it does the rebuild.

Finally, what is the situation re. disk redundancy whilst it's adding the disks?

Thanks

G
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Hossy

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ASKER
georgemason

Understood. So I guess the only question is, is there any risk in doing this at all? I'm in a position where I can move some of the more critical VMs off the array to local storage for the duration of the rebuild, which I think I might do in any case - but is this a risky process or run-of-the-mill?

(don't worry I won't sue if it goes wrong - just trying to get a feel for it!)

Your help has saved me hundreds of hours of internet surfing.
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ASKER
georgemason

All received and understood, thanks. Will move the sensitive machines off then run the upgrade.

Thanks to all for your contribution, will split the points. Will try to remember to update this with the results of the vdisk expansion to inform someone else in my situation another time!