There's (sortof) an additional wrinkle that needs to be noted:
When space reserve is used, snap reserve isn't needed - snapdrive sets this to '0' as part of its process, and you might want to consider it as well (makes the math a touch easier to handle).
Additionally, just because the volume is at 100%, doesn't mean you'll corrupt data - the space reserve is used to prevent this (it is configurable, doesn't have to be 100%, but setting it lower increases the risk of running out of room and causing write failures when snapshots are used). _Technically_, SnapDrive (if you're using it) will stop allowing snapshots to be created when the volume reaches 100%, but there's no other risk of data loss during failed write from over utilization.
From a performance perspective: ideally, volumes should be no more than 80% full with some workloads, 90% for others - that said, 100% full really isn't 100% full when space reservations are used (from a performance perspective).
Hope that helps a little bit....
Glenn
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From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Willeke, Jochen Sent: Thursday, September 04, 2008 6:54 AM To: David.Ashton@rullion.co.uk; toasters@mathworks.com Subject: RE: Noob...
Hi David,
as far as i can see, everything is as expected. When you have fractional_reserve set to 100 (%), as soon as you create snapshots on that volume, ontap will reserve 100% of the Luns size within the volume, to gurantee writes to complete successfully.
The maths show:
820GB * 0,8 (for snap reserve) = 656 GB
320GB Lun * 2 (for fractional reserve) = 640 GB
P = 640 / (656*100) = 97,56 %
Think ontap is doing some rounding, so 98% is correct.
Regards
Jochen
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From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of David.Ashton@rullion.co.uk Sent: Thursday, September 04, 2008 12:04 PM To: toasters@mathworks.com Subject: Noob...
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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