Jochen is correct. With a fractional reserve of 100% taking the first snapshot allocates 100% of the lun size within the volume. If you are pretty sure that you won't need all of that fractional reserve you can always set your fractional reserve lower.
An important fact to remember and it took me a while to figure this out is that the fractional reserve is only used once all other space in the volume is used. So that 100% of space that a fractional reserve of 100 reserves in the volume is only used once all of your snap reserve and all other free space within the volume is used, even though it's allocated and taking up space. You can think of the fractional reserve as a guarantee that you will have writes to the lun even when the volume reaches 100% full. So in your current setup where the volume is telling you you are at 98%, you are, but you could reach 100% and everything would keep working fine. Writes to the lun would continue to succeed, etc.... You just wouldn't be able to take new snapshots. At that time, when the volume was 100% full and you were still writing to the lun, then you would be using the fractional reserve.
It's a bit confusing and it took me a while to wrap my head around it but the Netapp guide that finally brought it home for me is called: Thin Provisioning in a NetApp SAN or IP SAN Enterprise Environment
Good luck, Romeo
On Thu, Sep 4, 2008 at 6:03 AM, David.Ashton@rullion.co.uk wrote:
Hi, please excuse my noobness, I've recently inherited a Netapp system or 3, I'm fairly new to SANs in general and netapp in particular. This isnt my full time gig (storage), its one thing amongst the 2 thousand other things I'm working on today, but I allocate a fair amount of time to figuring this stuff out.
I'm struggling with something I'm sure all netapp storage people go through, I've read the manuals, I've played around for about 6 months on the filers and I cant answer this.
I have a FAS3020. I have a volume, lets call it vol_bond. Its 820GB, 20% snap reserve. It contains one lun, which is 320GB. The space guarantee is volume, and fractional reserve is 100.
Currently, there are 5 snapshots, totalling 8GB. It is snap mirrored to another filer. Snapshots are created nightly, there are no problems with that. At weekends, after various backup activity, these grow to about 80GB, but we only keep 5 and they're deleted.
Its all up and running, everythings fine.
Except for the filer status which reports: /vol/vol_bond is full (using or reserving 98% of space and 0% of inodes, using 49% of reserve) and the df -r output is
/vol/vol_bondv8/ 687865856 670681368 17184488 335194536 /vol/vol_bondv8/ /vol/vol_bondv8/.snapshot 171966464 14140040 157826424 0 /vol/vol_bondv8/.snapshot
What am I missing? I thought I had this thing nailed but obviously not.
Dave Ashton
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