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

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

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

**********************************************************************

The information contained in this e-mail and any attachments are intended for the named recipient(s) only. It may also be privileged and confidential. If you are not an intended recipient, you must take no action as a result of receiving it, including, but not limited to copying, distributing and amending it. If this communication has been sent to you in error, please contact us immediately and do not show the communication to any other party.

Rullion shall have no liability whatsoever in respect of the content of the communication and makes no warranty as to accuracy. Any views or opinions presented are solely those of the author.

Viruses:- Although we have taken steps to ensure that this e-mail and attachments are free from viruses, we advise that in keeping with good computing practice, the recipient should ensure they are actually virus free.

**********************************************************************

________________________________________________________________________
This e-mail has been scanned for all viruses by Star. The
service is powered by MessageLabs. For more information on a proactive
anti-virus service working around the clock, around the globe, visit:
http://www.star.net.uk
________________________________________________________________________

WINCOR NIXDORF International GmbH
Sitz der Gesellschaft: Paderborn
Registergericht Paderborn HRB 3507
Geschäftsführer: Eckard Heidloff (Vorsitzender), Stefan Auerbach, Dr. Jürgen Wunram
Vorsitzender des Aufsichtsrats: Karl-Heinz Stiller
Steuernummer: 339/5884/0020 - Ust-ID Nr.: DE812927716 - WEEE-Reg.-Nr. DE44477193

Diese E-Mail enthält vertrauliche Informationen. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese E-Mail. Das unerlaubte Kopieren sowie die unbefugte Weitergabe dieser E-Mail ist nicht gestattet.

This e-mail may contain confidential information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorised copying, disclosure or distribution of the material in this e-mail is strictly forbidden.