Subscribe
Accepted Solution

Any best practices for adding disks to an aggreate

Hi All,

I just upgraded my FAS3240 to 8.1 to take advantage of the larger maximum aggregate size that 8.1 provides.

On each controller, I currently have 1 - SATA aggr composed of 34 – 2TB disks.  The current aggr is 2 raid groups of 17 disks (15 data/2 Parity).  On each controller, I have 25 -2TB spare drives which I would like to add to the existing aggregates. 

If I added the 25 drives to the existing aggr at the existing raid group size, I’d be adding 1 full raid group of 17 and a partial of 8.  This would then be a total of 4 raid groups (3 full and 1 partial).  What I would rather do is modify my existing raid group size to the max allowable of 20 so that when I add the 25 drives, 3 drives would go to each existing raid group (6 drives) and the remaining 19 would go into a new raid group.  The end result would be 3 raid groups(2 full and 1 partial of 19).  As I said, the latter solution is the one I’d like to go with and I think I’ll be just under the max aggr size.

Which solution would be better or does someone have a better solution?   I don’t want to potentially do something wrong and waste space I could use or worse off make performance worse.  Honestly, I don’t need the new drives added to the exiting aggr for space, but for IOPS so the last thing want is to make it worse.

Thanks in advance for the help.

Michael

Re: Any best practices for adding disks to an aggreate

Usually we prefer to keep all RAID group sizes even and the same number of disks per raid group for optimal performance.  When you add disks there can be a performance impact depending on the number of spindles added until those drives fill to the watermark of the other existing disks.  You can run reallocate to alleviate this but if running deduplication that isn't an option.  Ideally I would go with what makes the RGs all even sized and equal in size if possible up to the 90TB aggr limit on the 3240 with 8.1 (volume max is still 50TB though).

Re: Any best practices for adding disks to an aggreate

Hi Scott,

Thanks for the reply.  We are running deduplication, so it would seem I cannot reallocate based on your response.  I am not sure I understand what you mean by even sized RGs.  Setting my RG size to 20 would make them the most equal in size I would think as I'd end up with 2 x 20 and 1 x 19.  To accomplish that though, I would have to add 3 drives each to two my my original 17 RGs.  Thoughts?

Thanks 

Re: Any best practices for adding disks to an aggreate

That sounds like a good plan and yields well for usable. Going all 20 and a single 19 makes sense.

Sent from my iPhone 4S

Re: Any best practices for adding disks to an aggreate

Excellent. Thanks for the input. I think I’ll run with that then.

Re: Any best practices for adding disks to an aggreate

Dont forget you need spare disks. I didnt see any mention of them. I assume you got it covered. you dont need too many of the either so maybe

you could take 1 and fill all your RG with 20?

Eric

Re: Any best practices for adding disks to an aggreate

Yes, thanks for the suggestion. I had planned on leaving 1 spare per controller, so I think that should do. I am still just afraid that by growing my RG to 20 and throwing 3 disks in I will encounter some hot spindles.

Thanks

Re: Any best practices for adding disks to an aggreate

How much write percent is the aggregate? New data disks will be used for write regardless of raid group but number of disks can affect performance after adding.

Re: Any best practices for adding disks to an aggreate

Probably at least 90% write. These aggr’s are used for our snapvault location.

Re: Any best practices for adding disks to an aggreate

I would run a perfstat or statit to see disk utilization during a busy sample time. Then you can extrapolate disk utilization