What will happen if data size reach to total size of LUN ?

Posted on 2011-10-29
Last Modified: 2012-05-12
I am using VMware and three virtual machines are running with a SAN and Storage.

In case LUN size is 500 GB, and following virtual machines are running,
DomainController 200GB , ( Thick )
File Server 200GB ,(Thick)
Mail Server 200GB (Thin), currently, 50GB is used.

If Mail Server's data size become over 100 GB,
This means total data size reach to LUN size,
What will happen to DomainController, File Server and Mail Server ?

User cannot use Mail server ?
How about Domain Controller and Fileserver ?
What kind of impact will be given to those virtual servers ?
Question by:shouichi
    LVL 116

    Assisted Solution

    by:Andrew Hancock (VMware vExpert / EE MVE)
    It's possible that ALL the virtual machines will fail.

    Virtual Machines write logs, swap files, to the VM folder location, if there is no space left on the datastore, the Virtual Machines will halt and stop.

    Be very careful you do not use third party backup products that use Snapshots, as these also write to the datastore. Be careful and watch for snapshots.
    LVL 116

    Assisted Solution

    by:Andrew Hancock (VMware vExpert / EE MVE)
    You've probably not got a lot of free space on the LUN as you think you have, because of Logs, Memory Swap files (when the virtual machines are on, which is equal to the memory in virtual machines).

    So you will have less than 50GB currently available, due to logs, swap files.

    Monitor your Exchange server very carefully for growth, and check the procedures on Expanding the LUN, or creating a new LUN, and moving VMs to another LUN.
    LVL 2

    Accepted Solution

    Per VM, as they run out of space, they will fail.  The two thick provisioned will operate poorly then fail as they fill up.  The thin provisioned mail server will operate normally, even if the other two have failed due to space restrictions, until it reaches that extra 100GB growth you mentioned.  When it gets full, the mail server OS will "think" it has plenty of space, but disk I/O will become sluggish and finally halt as the limits of the expanding thin disk are felt at the ESX level.  

    vCenter, however, will start throwing warnings to you as the LUN fills up, and you can set those alerts to email you before things go bad.

    Ideally, however, since these are critical production VM's, additional SAN space needs to be available in the near future so when the limits are reached you can just extend the LUN and be safe.

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