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  • 1.  VM failed to boot due to insufficient Space on DataStore

    Posted Aug 29, 2016 11:57 AM

    Hello Everyone ,

    I am new to VMware

    On my Esxi host there are  6 virtual machines but one of them failed to boot due to insufficient space on the data store. But space assigned to the drives on the virtual machines are still  having lot of free space for example the vm which failed to boot has 125 Gb available on dirve C and 200 GB available space on drive D. I freed some space on the data store by moving some files to other data store and than vm was able to boot but after one day i had again the same problem of insufficient space the 10Gb that i had freed was used in just one day. I am unable to understand why there is a problem of of low disk space even the drives on the virtual machines are still empty.???

    Thank you in advance



  • 2.  RE: VM failed to boot due to insufficient Space on DataStore

    Posted Sep 07, 2016 08:03 AM

    Hello,

    "I am unable to understand why there is a problem of of low disk space even the drives on the virtual machines are still empty.???"

    You are confusing two things:  what happens inside the VM, storage-wise, does not need to have any relation to what happens on the Hypervisor / physical storage level. Your VM can have all the free space in the world, but if the underlying datastore is full, or nearly full, you get in trouble.

    I assume you provisioned the virtual disks of the VM's as "thick". This means that a VM Disk of say, 50 GB in size, really, physically allocates 50GB on the datastore. What is happening inside the Guest OS is totally irrelevant. The VM has 50 GB available and can do whatever it wants. ESXi does not care how much free space there in inside the VM as it, the hypervisor, has 50GB allocated.

    If a datastore runs full, ESXi won't be able to start VM's because during power-on of a VM, a swap-file get's created (size = VM memory size) and if this space is not available, the VM cannot boot.

    Again, this is assuming you used "thick" as the allocation method. There is also a "thin" method which works differently.

    It is a best general practice to leave about 15% free space on a datastore at any one time. 10GB free (if I understand you correctly) sounds like "nearly full". A VM with 4 GB of vRAM would trigger the creation of a 4GB Swap-file (on the VMware level, has nothing to do with the VM's OS which has it's own swap-file inside of it) and that would mean 10GB - 4 GB is 6 GB free. That is really way too little free space. Filesystems need "free space to breathe".

    By the way, I assume you are using VSAN (because you started this topic in the VSAN Area) and VSAN needs lot's of free space to work and to be able to cope with disk/host-failures etc. etc. etc.

    You write that you are new to VMware. First of all:  Welcome. Second: the question you ask is very basic. You will run into many, many more questions and posting them on forums is not a quick way to get answers and build up knowledge. I really suggest following a basic training to aquire knowledge of this sort of fundamental stuff.