RHEVM: Bug ? NFS based Export Storage domain reporting incorrect filesystem usage

Latest response

Hi

 

Found a possible bug in 3.0.7.  

Support case 00724728

 

RHEV Version:- 3.0.7

 

Test :-   Export a VM or template to your NFS based Export storage domain. Examine the change in "Available:" and "Used:" displayed in the General tab for your Export storage domain.

Then remove/delete that same VM or template from the Export storage domain. Examine the change in "Available:" and "Used:" displayed in the General tab for your Export storage domain.

 

 

Expected Result:-

The figure in "Used:" should be zero.

 

Actual Result :-

The figure in "Used:" still reflects the figure prior to to the removal of the exported VM or template."

 

Thanks

Responses

Hi Richard,

 

If you look at the NFS export manually, do you still see the images there, even if they should have been removed? Have you given this a bit of time to actually wipe the images and refresh the SD?

The General tab for my Export SD says :-

 

Size:            236GB

Available:     144GB

Used :          92G

 

The actual filesystem reports :-

 

lhprevm01.pgds.local # df -h /rhev-export/export
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/SPlhprevm01--appVG-rhev--export
                      237G   81G  145G  36% /rhev-export/export

 

But a du show something different :-

lhprevm01.pgds.local # du -sh /rhev-export/export
64K     /rhev-export/export
 

lhprevm01.pgds.local # cd /rhev-export/export/abf71520-2803-44d4-9dcb-fa4afefe0efc
lhprevm01.pgds.local # du -sh *
12K     dom_md
4.0K    images
12K     master
12K     v2v.k3Ld1_Us

 

It's been 20mins since I removed the VM Image from the Export SD.  
 

It's reducing but very slowly....

 

Size :                   236GB

Available :            184GB

Used :                   52GB

 

/dev/mapper/SPlhprevm01--appVG-rhev--export
                      237G   41G  185G  18% /rhev-export/export
 

 

Stopped reducing.  Remains the same as above.

Anyway, we've figured out the problem.  Feel a bit of a dimbo!

It is because the default amount of reserved blocks in a standard ext3/4 filesystem is set to 5%.

The df command knows not to show the reserved blocks in the "Used" column, whereas RHEV simply subtracts "Avail" from "Size" to calculate "Used" and suddenly 60M in df shows as 12G in RHEV. This is misleading.

 

We proved this theory by tuning the reserved block down from 5% to 0.1% on the export and the figures now look correct on RHEV.

 

Moreover, 5% of reserve is overkill for a modern ext3/4 filesystem. Perhaps you should advise on a smaller figure to take into account the size of filesystems supported these days and their stability.

 

You may wish to review my "Guru" status  ;)

Support case updated but left open in case of any further action.  -  Thanks

We'll create a "dimbo" badge for you as soon as possible, Rich. Until then you can keep "guru" ;)

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