Recommented sizing for root volume

[jasonwo]

Hi,

I am planning the configuration for my filers. I am doing some research on the recommentation on the root volume sizing. I have 2 approaches now:

1. Create a large 14 disks raid-dp aggregate to host both the root volume and other application volumes.

2. Create a 2 disks raid 4 aggregate to just host the root volume. Create another aggregate for application volumes.

# 2 sounds reasonable as I heard there is administration advantages on separating the root volumes and the application volumes into different aggregate. But at the same time, I find that there is paper (http://www.peripheralstorage.com/NetApp/pdfs/SynchronousSnapMirror.pdf) saying that it's not good idea to configured root aggregate as raid 4 since the number of disk can't provide adequate write performance on snapmirror. Any thoughts?

Thanks,
Jason

[thomas_glodde]

Hi,

we usualy integrate the root volume into the data aggregate on small machines (FAS20X0 and small FAS31x0 configurations) but tend to seperate it on bigger machines (6shelves+, FAS31x0,FAS60x0).

Regarding snapmirror/syncmirror, the root volume doesnt write that much stuff so 2 disks are quite sufficient usualy.

Kind regards

Thomas

[scottgelb]

There are some existing post on this that is a good reference.  http://communities.netapp.com/message/28177#28177

The issue with a 2 drive root aggregate (raid4) is that you don't get hot upgrades of disk firmware since that requires dual parity.  You could add a disk, hot upgrade, remove the dual parity and zero it, but that is a lot of work every time you upgrade firmware.

The recommendation for more than 3 drives (7 drives) for snapmirror is when we are using snapmirror sync/semi-sync where the cplogs and nvlogs get written to the root aggregate and more spindle I/O is needed.  It isn't a good idea to run synchronous snapmirror with a small root aggregate.  With async snapmirror this is not an issue.

Per the above link you will find detailed discussion and debate on a separate or combined root aggregate.  I tend to create separate but when a smaller system I agree it is a big cost not worth the rare risk of aggr failure.  However, note the 8.0 64-bit discussion.  A root aggregate must be 32-bit.  So, if you want all 64-bit large aggregates in 8.0, you will need a separate 32-bit root aggregate.

[aborzenkov]

The recommendation for more than 3 drives (7 drives) for snapmirror is  when we are using snapmirror sync/semi-sync where the cplogs and nvlogs  get written to the root aggregate and more spindle I/O is needed.

In current DataONTAP logs a written to aggregate that hosts target volume.