[geeks] recipe for Linux / iSCSI / thin provisioned space

[Patrick Giagnocavo]

On 9/14/2010 11:22 AM, der Mouse wrote:
(2) disk
> space overcommit.
> 

This is the key driver for thin provisioning.  The more systems you have
using 1 iSCSI filer, the more data you save.

E.g. 4 systems each with 12 VMs (48 VMs), all using 1 iSCSI server with
4.8TB:

thick provisioned = each VM can have 100GB; if each VM uses only 96GB
(4GB unused) on average, then wastage is 4*48 = 192GB.  Plus, some will
need more space and then you have to go buy another filer even though
you have almost 200GB unused on the current one.

thin provisioned = give each VM 1TB disk, monitor usage and re-juggle
onto 2nd filer (as you would under thick provisioning) at a much later time.

That system's disk usage will follow a gaussian distribution (bell
curve) may or may not be true, but surely some will use less than
planned and some will need more.  Thin provisioning allows for much more
flexibility.

I hope my explanation serves ...

--Patrick