Volume used and LUNS

[jblake]

I’m a bit confused with the space some volumes are reporting.

I have

• 710Gb Volume (Fractional Reserve 20% / Snap Reserve 0)
• The volume contains a 460Gb lun of which 452GB  is being used.
• My snapshots report 117 Gb used

Therefore I would expect space used by the volume to be

Volume – Lun used size – FractionalReserve  - SnapShot Used

710 – 452 – 142 – 117 = -1

The volume actually reports 669Gb used and 41Gb free?

So from the figures above resulting in -1, I'm assuming that I'm using some of my Fractional Reserve for snapshots, however each snapshot is only about 15gb so I would expect the volume available space to get to 0 before Fractional Reserve starts being used. I can't see how you can see how much of the Fractiona Reserve is actually being use.

I’m sure I’m doing something wrong but just can’t see it.

Thanks

[peter_lehmann · Accepted solution]

Hi

The Fractional reserve is a setting for how important it is for the snapshot of this LUN to be able to be created. Set it to 20% and it will "reserve" 20% of the size of the LUN to "guarantee" the creation of a snapshot that needs 92G of space. If you create a snapshot that nedds more space then 92G, it will fail...

Try this math:

vol = 720G

LUN = 460G

free1 = 260G

snap used = 117G

free2 = 143G

Fractional = 92G (20% of 460G)

free3 = 51G

space used  =  460 + 117 + 92 = 669

Hope this helps,

Peter

[jblake]

Brilliant I always thought that Fractional Reserve was based on volume size as its set as volume level not on Lun size.