Confusion about storage free space reporting - Ontap vs Windows

[ALEDOCHOWSKI]

Hello,

I've encountered an issue which i find difficult to understand, so please guys enlighten me on how to deal with it

There are 2 LUNs presented from my filer to my Windows Server cluster. For the first one, Windows Server reports free space larger than Ontap does. For the other one, Windows Server reports free space smaller than Ontap does.

The former is pretty obvious - since Ontap doesn't know what goes on inside the LUN, it reports the space freed up from within Windows as still being occupied from the filer perspective.

But what about the latter? Why does the filer think the LUN has more free space than it really does?

Whom should I trust ultimately?

Both LUNs are thick provisioned, used for Hyper-V CSV and reside on separate volumes. Both volumes are thick provisioned, have deduplication turned on, fractional reserve = 0, snap reserve = 0, snapshots turned off.

Thanks in advance

[aborzenkov]

NetApp has no way to report on a free space in a LUN. Please paste exact command invocation and output you use to see NetApp report.

[ALEDOCHOWSKI]

See below... I'm referring to the "Occupied Size" property.

lun show -v /vol/bss_csv_hvntn_os/bss_csv_hvntn_os1/bss_csv_hvntn_os1.lun

        /vol/bss_csv_hvntn_os/bss_csv_hvntn_os1/bss_csv_hvntn_os1.lun    5.9t (6487278336000) (r/w, online, mapped)

                Serial#: D14Mr$CH248l

                Share: none

                Space Reservation: enabled

                Multiprotocol Type: hyper_v

                Maps: hvntn_csv=0

                Occupied Size:    5.3t (5867480559616)

                Creation Time: Tue Feb 19 14:43:43 CET 2013

                Cluster Shared Volume Information: 0x3

lun show -v /vol/bss_csv_hvntn_os_HA/bss_csv_hvntn_os_HA_1/bss_csv_hvntn_os_HA_1.lun

        /vol/bss_csv_hvntn_os_HA/bss_csv_hvntn_os_HA_1/bss_csv_hvntn_os_HA_1.lun    2.0t (2199036833280) (r/w, online, mapped)

                Serial#: D14Mr$CH248r

                Share: none

                Space Reservation: enabled

                Multiprotocol Type: hyper_v

                Maps: hvntn_csv=2

                Occupied Size:    1.7t (1872039890944)

                Creation Time: Mon Sep  9 13:30:42 CEST 2013

                Cluster Shared Volume Information: 0x3

Also System Manager shows the same:

And here's how these LUNs look (respectively) inside Windows Server:

[aborzenkov]

Most probably this is due to "sparse files". I.e. When you create 100G file you do not really write anything, so from NetApp side it occupies nothing. First when you start writing to this file it starts consuming space on NetApp.

[ALEDOCHOWSKI]

Ha, thanks, this indeed may be the cause, since the LUNs host virtual disks