I don't read this document the way you do.
It says that if, on a 2020, you want an aggregate larger than 8TB, you need to either:

1) create a separate root aggregate
2) maintain 2 spare disks

The separate root aggregate requirement does not mean you can't have user data on it - in fact, the system has no way to audit that anyway.
Personally, I'd just leave two spares.  You could use a raid 4 root aggregate, but then you still need a separate spare... so, most efficient storage-wise is to leave two spares.  That only consumes one extra parity disk.


-----Original Message-----
From: owner-toasters@mathworks.com on behalf of Milazzo Giacomo
Sent: Tue 1/20/2009 9:02 AM
To: Glenn Walker; toasters@mathworks.com
Subject: R: 7.3.1 and 2020 nonsense :-)

Maybe something has been not clear for you. The issue is for this nonsense 2020 usage of 7.3.1.

For 2020 and 16TB aggregate only: you must create a SEPARATE aggregate raid dp that will have to contain THE ROOT ONLY, no other volumes, no user data.
If you want you could also use R4...but with 2 spares. The result is the same. For a 2020 using 1 TB SATA disk I will waste 3 TB for root!!! Nonsense...unuseful, ridicoulous...what else? :-)


________________________________
Da: Glenn Walker [ggwalker@mindspring.com]
Inviato: martedì 20 gennaio 2009 17.27
A: Milazzo Giacomo; toasters@mathworks.com
Oggetto: RE: 7.3.1 and 2020 nonsense :-)

I don't see the issue:

Create massive aggregate, use RAID-DP and leave 2 spare disks.  Put all data in the one aggregate.

We (as a general rule) do not use a separate aggregate for our root volumes - we just maintain a healthy number of spares and use RAID-DP.

Glenn

________________________________
From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Milazzo Giacomo
Sent: Tuesday, January 20, 2009 7:09 AM
To: toasters@mathworks.com
Subject: 7.3.1 and 2020 nonsense :-)

Hi all,

reading this from 7.3.1 release note I've been really beated from this. I was thinking to a 2020 full of 1 TB SATA. To have a 16 TB aggregate I should waste 3 TB for few gigs of root! :)
Luckly I don't think that somebody will suggest a 2020 to manage 16 TB of data!!! :)

Bye

Increased aggregate capacity for FAS2020 systems
Beginning with Data ONTAP 7.3.1, FAS2020 systems support aggregates up to 16 TB raw capacity,
provided that the root volume is hosted in a dedicated aggregate (that is, one that contains only the root
volume and no user data).
Note: An alternative to maintaining a dedicated root aggregate is to maintain two spare disks. A
dedicated root aggregate configuration of three disks is the recommended best practice for all systems.
However, if such a configuration is not practical in your environment, you must maintain two spare
disks if you configure your FAS2020 system for aggregates larger than 8 TB raw capacity.
If you do not configure aggregates larger than 8 TB raw capacity on your FAS2020 system, the
conditions for two spare disks or a dedicated root aggregate do not apply.
For more information about FAS2020 systems' storage capacity, see the System Configuration Guide.



Dott. Giacomo Milazzo
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Technical Account Manager
Sinergy SpA
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. Giacomo.Milazzo@Sinergy.it