Hi Everyone,

thank you for the very beneficial lesson. So I understand now that fractional reserve is to allow for new writes to a lun (especially if you are taking snapshots)

But what is the best way to set this? --- It appears that vol fractional reserve is set at the CLI level, but seems like I can also set this up in SME & SD. If I set fractional reserve to 50%, it shows in SME/SD that all the luns are set to 50%. But what does this do to checking/unchecking 'lun space reserve' in FilerView --- What is the point of doing this?

I have read all the tech docs from ntap, and they only explain these in the most convulted way possible. Wish they put a doc on best practices on when to turn these on/off.

Is anything ever written & deleted from the fractional reserver space?? Or is it just there, in case things go haywire?



On 3/8/07, Fox, Adam <Adam.Fox@netapp.com> wrote:
Don't feel too bad...space reservations takes time to digest.
 
Space reservations don't affect your ability to mount snapshots.  Doing fractional reserves is one way
to handle snapshots on LUN volumes.  Doing so carries some risk in that the volume can run out of space
before the LUN does.  But if you know your change rate, you can use fractional reserve if it fits your needs.
 
Another method you will find customers on 7.1 and later using is to not use space reservations at all, leaving a
reasonable amount of free space in the volume, then setting up policies for autogrow and/or auto snapshot delete
in case you run over.
 

-- Adam Fox
NGS Tools Developer
adamfox@netapp.com

 

From: owner-dl-toasters@jhereg.corp.netapp.com [mailto:owner-dl-toasters@jhereg.corp.netapp.com] On Behalf Of Steven Mandrake
Sent: Thursday, March 08, 2007 12:16 AM
To: toasters@mathworks.com
Subject: mounting snapshots

Hello,

I am having the hardest time understanding fractional space reservations for volumes and lun space reservations.

If I reduce fractional space reservations to a volume that contain luns, what happens to lun space reservations? Is there a way to throttle lun space reservations -- as far as I can tell it's just a check box in Filerview....

The main question I have is --- does setting fractional space reservation affect my ability to mount snapshots. I assume that mounting snapshots does not take any space since it's all read-only.... or am i wrong in assuming this?

My assumption right now is that fractional space reserve is there if I ever need to mount a snapshot to be read/write --- am I dead wrong?

Thanks,
Steve