Thin operational considerations for GUEST OS environments

Question

Hi all, I have just reviewed with my customer the different types of thin interaction that are available with a variety of operating systems and the Symmetrix platform (namely VMAX).  This has been well received but they followed up with a question that I would welcome input on. Basically, do we need to consider any 'thin friendly' operations in an OS that is deployed via a vmware guest?  ie: Windows 2012 or RHEL 6.x in a VM.  Where the OS is thin aware and can do PUNCH/Write SAME type operations. My current response is there is nothing that you enable/setup (regular fstrim, disk monitoring reclaim) in the guest OS around disk usage as ESX is aware of what actual storage is being consumed and interacts with the actual storage array in a thin friendly manner (assuming THIN or LAZY zeroed thick vmdk). However, does anyone know if the GUEST does trim/reclaim/punch operations to the virtual SCSI disk if VMware will recognize this activity and operate accordingly with the underlying storage (notifications, etc?) Thank you Doug

codyhosterman · Accepted Answer

For virtual disks, VMware blocks (or rather can't/doesn't) interpret UNMAP or WRITE SAME sent from Guest OS's. These type of functions only work with raw device mappings. So the short answer is no.

That being said, in vSphere 5.1 VMware introduced the Space Efficient Sparse Virtual Disk that can reclaim space from guest OS filesystems on a virtual disk and forward that reclaim to the array using UNMAP.

I'd check out these docs for some more information:

http://www.emc.com/collateral/hardware/white-papers/h6813-implting-symmetrix-vrtl-prvsning-vsphere-wp.pdf

http://www.emc.com/collateral/software/white-papers/h6730-virtual-provisioning-space-reclamation-wp.pdf

codyhosterman · Answer

Thanks Matt, I meant to say that but forgot. Important point

mattcowger1 · Answer

In addition to Cody's (absolutely correct) response, its worth noting that SASVD's are only useable (today) in certain VDI/vCloud environments.

VMware

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