Difference between "Disk space used on host" versus "Disk space"+"Virtual memory"?

Submitted by yngens on Wed, 10/08/2014 - 06:51

Running cloudmin list-systems --host host.domain.tld --multiline --bytes | grep Disk for one of our guest systems is giving:

  Disk space used on host: 12096372736
    Disk limit over period: 112.10 GB hours (433310861885440 byte seconds)
    Disk used over period: 112.10 GB hours (433310861885440 byte seconds)
    Disk average over period: 10942193481 bytes
    Disk space: 10310975488
    Disk space free: 5375299584
    Disk space used: 4935675904

Thinking about difference between "Disk space used on host" and "Disk space used" I thought that maybe "Disk space used on host" is a total of "Disk space"+"Virtual memory", however obtaining total virtual memory for the same system by running ssh -p 19437 root@216.218.219.92 cloudmin list-systems --host host.domain.tld --multiline --bytes | grep memory command gives:

    Real memory: 1587851264
    Real memory free: 1219117056
    Real memory used: 368734208
    Virtual memory: 1608511488
    Virtual memory free: 1608511488
    Virtual memory used: 0

so if I add

Disk space: 10310975488 + Virtual memory: 1608511488

then I'll get 11919486976 bytes, which is slightly less than Disk space used on host 12096372736 bytes. Why is this difference and what is what? We need to clarify this because we are confused which one of them to use in our back-end script. Thanks!

Status: 
Closed (fixed)

Comments

Submitted by yngens on Wed, 10/08/2014 - 07:18

Similar confusion between "Memory limit" and "Real memory". In our case they are showing different numbers:

Memory limit: 1610612736 Real memory: 1587851264

Submitted by JamieCameron on Wed, 10/08/2014 - 12:15

"Disk space used on host" is the amount of space the VM's virtual disk images take up, while "Disk space" is the usable size of the filesystem inside the VM (which is smaller due to filesystem overhead).

"Memory limit" is the limit set for the VM, while "Real memory" is the total RAM available as seen inside the VM (again smaller due to kernel overhead).

Submitted by yngens on Wed, 10/08/2014 - 19:16

Thanks for explanation, now we know which ones to use on our scripts. Marking this one as closed.