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Netapp Spare

Posted on 2012-08-31
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Last Modified: 2012-10-25
EE,

I have a netapp 2040 dual controller.

Spares are global for all aggr's but dedicated to that one controller.

So if I have Raid_DP which can survive double disk failure, don't I need two spares per controller? It just seems like everyone else is using 1 spare with Raid_DP, that doesn't make sense to me or am I missing something?

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Question by:snyderkv
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by:Busbar
Busbar earned 668 total points
ID: 38353676
do you mean that you need to add another spare, by default the aggr. will use all the disk and create 1 spare, you can add another one to protect against double failures.
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by:robocat
robocat earned 668 total points
ID: 38353724
The recommended number of spares (by Netapp) is 2, but on small systems you can get by with one.

The reason for 2 spare disks: a spare could fail during rebuild. There's also a feature called "maintenance center" that tests disks before failing them, and this requires at least two spares.

So on a 2040, 1 spare/controller is probably enough.
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by:snyderkv
ID: 38353752
Robocat,

But what if Raid_DP has two disk failures. It won't use the other controllers spare will it?
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by:Paul Solovyovsky
ID: 38354238
2 disk failures on an aggr will still allow it run.  You can also get by with a single spare. If you have a shelf you can move split the vol0 hosting vol0 between the two, this will allow you to have 2 aggrs on two controllers and save at least 3 drives versus having 2 aggrs on the internal storage and 1 on shelf.
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by:snyderkv
ID: 38354542
I wouldn't do that because storage is not a problem for us. The issue is simply best practice for raid_dp. If I have to run at reduced speeds while ordering a second disk spare, then that may not be acceptable but I doubt it will run that much slower if at all.

Thanks
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by:Busbar
ID: 38354558
the spare is not per controller it is per aggregate, multiple aggregates means multiple spares
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by:Paul Solovyovsky
ID: 38354605
I agree.  If we split the the aggregates containing vol0 for each controller on a 2000 series unit we can save quite a few drives. Typically netapp sends out the units with both vol0 on the internal drives and if you have a shelf you create a 3rd aggr.  If there is a shelf we can move one of the controller aggrs over to the shelf and use it to serve data so that we free up 3 drives on the internal unit, process is fairly easy.
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by:snyderkv
ID: 38354647
Busbar, could you back that up with docs? Because I could of swore it was per controller (global) as I read it. Which means you can have 10 Aggrs and one global spare which will provide for any of the 10 Aggrs given they are the same speed and type drives.
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Paul Solovyovsky earned 664 total points
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@snyderkv: First, hope is gong well where you are, can be rough out there.

With RAID-DP performance reduction is negligible in most cases.  The only times we have seen issues is when the aggr is over 90% which is normal since the Netapp doesn't have as much room to write to.  Having 2 spares is always a good thing to have but a lot of our customers use 1.  I would have 2 in environments with SATA drives as they can take a lot longer to rebuild.
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by:snyderkv
ID: 38354724
Thanks Paul, I'll stick to the standard build sheet since it's not a huge deal either way. We only use 15k SAS because of exchange and other high IO services

Things are going great, whether is nice this time of year and I'll be cramming on SRM shortly for some of these coop sites. That will be new. Expect more posts hehe
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by:robocat
ID: 38354735
>But what if Raid_DP has two disk failures. It won't use the other controllers spare will it?

no, it will only use the disks that it has ownership of.

>the spare is not per controller it is per aggregate, multiple aggregates means multiple spares

This in incorrect. A spare disk is by definition a disk that is NOT assigned to an aggregate.

If you have different types of drives/sizes/speeds, you do need at least one spare of each.
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by:snyderkv
ID: 38535603
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