Hi Thu Ya,
Do you use FC or iSCSI?
You can read the vSphere Documentation about booting ESXi from FC SAN, iSCSI, or FCoE:
vSphere 5.5 Documentation Center - Booting ESXi from Fibre Channel SAN
vSphere 5.5 Documentation Center - Booting ESXi with Software FCoE
vSphere 5.5 Documentation Center - Using ESXi with iSCSI SAN
Make sure your HBAs/iSCSI NICs and arrays/storage support booting from SAN/iSCSI
Yes you will need to request a separate LUN for your 10 ESXi hosts means 10 LUN (some vendor requires LUN ID 0).
Be sure to exclusively mask the boot LUN to the host, boot-from-SAN boot LUNs must be exclusively masked to their host.
The host can get the wrong identity from an incorrect LUN so you should configure single-initiator zoning in boot from SAN.
The Emulex and QLogic BIOS can become unresponsive if several other initiators are in the same zone and you try to select a boot LUN.
For the LUN requirements, you can prepare ~6GB LUN for each LUN as described in the vSphere 5.5 Documentation Center - ESXi Hardware Requirements
Storage Requirements for ESXi 5.5 Installation
Installing ESXi 5.5 requires a boot device that is a minimum of 1GB in size.
When booting from a local disk or SAN/iSCSI LUN, a 5.2GB disk is required to allow for the creation of the VMFS volume and a 4GB scratch partition on the boot device.
Some related KB as below:
VMware KB: Preliminary Configuration for Boot-from-SAN
VMware KB: Identifying ESXi/ESX boot LUNs for Boot From SAN configurations
How to configure ESXi to boot via Software iSCSI? | VMware vSphere Blog - VMware Blogs
Message was edited by: Bayu Wibowo