In most virtualization project, regardless of hypervisor, I realize that there are many questions concerning the size and number of LUNs. Many administrators choose to consolidation, others prefer the isolation.
Below I describe the characteristics, pros, cons and recommendations on creating LUNs for virtualized environments.
In isolated storage, each virtual machine, regardless of its size or importance to the business, has a unique LUN. In some cases, the same virtual machine comes to have two or more LUNs used for C and D units, for example. Keeping a virtual machine by LUN is possible to obtain an improvement in performance because there is no competition in the LUN on the other hand you can get the maximum supported by the hypervisor, and there is a misuse of resources, because the free space on a LUN can not be used by another virtual machine.
An environment with 50 virtual machines becomes complex and very difficult to administration, because the storage will have 50 LUNs and the hypervisor 50 datastores / volumes, in other words, before creating a new virtual machine, you must create a new LUN, submit to the hypervisor and configure it.
- If a problem occurs with the LUN, will affect only a virtual machine;
- Possible improvement in performance, there is no competition in the LUN.
- Misuse of resources;
- Complex environment;
- Much time is dedicated to managing and maintaining the environment.
In consolidated storage, all virtual machines are stored in a single LUN. With this configuration, there is a better use of resources, maintenance and also in the management of the environment. However, competition in the LUN is great, may cause decreased performance of virtual machines.
An environment with 50 virtual machines becomes simple and easy administration, because the storage will have only one LUN and the hypervisor a single datastore / volume.
- Better use of resources;
- Simple environment;
- Management and facilitated maintenance.
- If a problem occurs with the LUN, will affect all virtual machines;
- Possible reduction in performance, a lot of competition in the LUN.
Okay, what the size of the LUNs and storage type should I use?
You can see the pros of one type of storage is the cons of the other, so it is not possible to adopt a standard storage type and size of the LUN, all depends on the environment and needs. VMware recommends using a mix between the types of storagehaving consolidated storage with some privacy, so the LUNs can be large enough to hold X amount of virtual machines, but it also depends on the hardware (size disk, rpm, cache controllers, etc.) and virtual machines (avoid storing SQL and Exchange servers on the same LUN, for example). Most manufacturers suggest to perform a full analysis of the environment, in view of the hardware, needs and growth prospects, in order to then stipulate the amount and size of LUNs.
There are some precautions that should be taken before and after the creation of LUNs:
- Knowing the limitations of hardware;
- Knowing the size, number of virtual machines and estimate the possibility of growth;
- Separate LUNs groups by dividing transport protocols (NFS, iSCSI, FC, etc), disks (SATA, SCSI, SAS, SSD, etc.) and virtual machines that require more I/O.