That depends greatly on the values of N and n, as well as the RAID group size of the aggregate. Done according to best practices, there will be almost no difference. Done poorly, it can make all the difference in the world.
My personal view (I'm in no position to speak officially for NetApp) on this to add disks to an aggregate in one of 2 multiples:
1) a whole RG at a time 2) half a RG at a time.
This typically allows for a sufficient number of free disks such that you should not expect any noticable performance difference. I realize that not all sites can implement this, but let's look at a worst practice:
N = n+1
Fill up the aggregate, then add 1 disk. Ouch! This hurts! So you've seen what I consider to be the best case for adding space, and you've seen the worst case. So how close you are to these extremes should give you can idea of what to expect.
I know this isn't a simple answer, but I believe it to be accruate.
-- Adam Fox adamfox@netapp.com
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From: Suresh Rajagopalan [mailto:SRajagopalan@williamoneil.com] Sent: Monday, January 22, 2007 12:46 PM To: toasters@mathworks.com Subject: Aggregate expansion
Is there any difference between creating an aggregate on a certain number of disks (say n) , and then later expanding the aggregate to N disks, as opposed to creating the initial aggregate on N disks?
Suresh
All;
It was my understanding that you can alleviate the pain caused by an uneven expansion of disks as mentioned below by performing a wafl scan reallocate, anyone have info to contrary?
Glenn
________________________________
From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Fox, Adam Sent: Monday, January 22, 2007 2:30 PM To: Suresh Rajagopalan; toasters@mathworks.com Subject: RE: Aggregate expansion
That depends greatly on the values of N and n, as well as the RAID group size of the aggregate. Done according to best practices, there will be almost no difference. Done poorly, it can make all the difference in the world.
My personal view (I'm in no position to speak officially for NetApp) on this to add disks to an aggregate in one of 2 multiples:
1) a whole RG at a time 2) half a RG at a time.
This typically allows for a sufficient number of free disks such that you should not expect any noticable performance difference. I realize that not all sites can implement this, but let's look at a worst practice:
N = n+1
Fill up the aggregate, then add 1 disk. Ouch! This hurts! So you've seen what I consider to be the best case for adding space, and you've seen the worst case. So how close you are to these extremes should give you can idea of what to expect.
I know this isn't a simple answer, but I believe it to be accruate.
-- Adam Fox adamfox@netapp.com
________________________________
From: Suresh Rajagopalan [mailto:SRajagopalan@williamoneil.com] Sent: Monday, January 22, 2007 12:46 PM To: toasters@mathworks.com Subject: Aggregate expansion
Is there any difference between creating an aggregate on a certain number of disks (say n) , and then later expanding the aggregate to N disks, as opposed to creating the initial aggregate on N disks?
Suresh
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Fox, Adam -
Glenn Dekhayser