Thin or thick? Selection of Virtual disk format

Since it is the choice question, or first say the answer. This is more familiar to the concept of Thin/thick students can not waste time to see the long speech behind.

* If you have to use FT, you can only choose Eagerzeroedthick.

* If the pursuit of the best application can not consider space occupancy, choose Eagerzeroedthick

* If you want to maximize the use of space, and the growth of the disk is controllable, you can choose the thin format

* If you do not want the excessive allocation of space (oversubsribe) to cause potential problems, you can choose the default thick (Zeroedthick)

* If you want to have no negative performance impact, you should not choose thin. Concrete reasons see humble wen "thin or thick (continued), empirical new conclusion!" "(2010/3/11 Supplement)

"Format of virtual disks"

Virtual disks are available in 3 formats: (1) thin provision (2) thick (also known as Zeroedthick) (3) Eagerzeroedthik

(1) Thin provision is an on-demand format, created when the virtual disk will not be allocated to all the required space, but as needed, VMDK automatically increase and use these new space on the side of zero; the true size of the vmdk file is not equal to the size of the virtual disk created, And just equal to the size of the actual data. (Zero is to write 0 to disk whitespace, can be understood or translated into initialization).

(2) Zeroedthick format, allocated to all space at the time of creation, VMDK file size is equal to the size of the virtual disk created, the free space on the virtual disk is occupied, but the free space (empty spaces) does not zeroed, need to use when zero. Because disks must be zero on the first write, this type of disk has a slight I/O performance loss when the first disk block is written.

(3) Eagerzeroedthick, allocated to all spaces at creation time, vmdk file size equals the size of the virtual disk created, and the free space on the virtual disk is preloaded. In addition, when you create a disk, all blocks of data are initialized (zero), which takes more time. This format of the disk because it has been zero, use no longer need zero, so the first time to write data to disk block performance is better. Enable FT must use a virtual disk in Eagerzeoedthick format (it will be converted to this format if not previously)

For example, 1 500GB virtual disks, of which 100GB is used, and 400GB unused space. Thin format vmdk file size is the 100gb,zeroedthick and eagerzeroedthick format vmdk file size is 500GB, but Eagerzeroedthick 400GB unused space has been initialized, have been filled in 0, and the Zeroedthick 400GB unused space has not yet been initialized.

When VI3.5, the GUI interface does not provide a choice of the type of virtual disk, but instead uses the default type directly, the default is as follows:

* Create a new virtual disk on the Vmfs datastores, default to thick (Zeroedthick)

* Create a new virtual disk on NFS Datastores, default to Thin

* Deploy a VM from the template defaults to Eagerzeroedthick

* Clone a VM defaults to Eagerzeroedthick

That's why ESX3 is quick to create a new virtual disk, but it takes a lot of time to deploy or clone from a template. In reality, most of the virtual machine is created by deploying or cloning an existing virtual machine from the template, so in the esx3.x era, thin format is not very useful, virtual machine disk is basically eagerzeroedthick format.

However, the Vsphere4,vmware has made significant improvements to this, from the template to deploy a VM or clone a VM no longer default to Eagerzeroedthick, but there is a GUI allows you to choose thin or thick (that is, Zeroedthick).