I have been reading through the forums looking for best practices on carving up a brand new SAN for use with a brand new IBM BladeCenter. We are coming from multiple standalone ESX hosts and we purchased an IBM BladeCenter with 18 blades (13 HS20 two-way and 5 HS40 four-way), and a Hitachi AMS500 SAN with close to 4TB of space available to us. This is for a QA/Dev lab and the SAN primarily contains SATA disks for the majority of the VMs we will be running. We have about 1TB of FC we're reserving for performance testing. My question relates to the SATA disk space we have available to us.
We will be doing 100% boot from SAN. None of the blades will have locally attached storage.
So far here are my assumptions which have been confirmed by the forums. If anything seems wrong please let me know:
1) We will want to carve out one LUN for each of the ESX boot volumes.
2) We will want to carve out one large data storage LUN for every 10-15 VMs that will be running off it. This LUN can be shared among blades (we only plan to have a max of 6-8 VMs running per blade, hence the LUNs will need to be shared). The LUNs available to ESX will need to be set to Public access mode.
3) Each LUN will be available to all blade servers. However only two or three blade servers may be running VMs from a given LUN.
My questions are as follows.
1) Is it better to create fewer large raid groups and many small LUNs, or should the raid-group to LUN ratio be more 1:1 for performance reasons? I assume a LUN spanned across a RAID group will be striped against all the disks in the group. So two LUNs created on the same raid group will span all of the spindles, causing a decrease in performance.
2) Is it better to carve many smaller LUNs or a few larger LUNs for VMDK storage? Larger LUNs would be easier to manage, but in terms of performance, what have people experienced?
3) What size boot LUN would you carve out for each ESX boot volume?
4) If you had 18 blades and 4TB of disk space over maybe 25-30 disks, how would you setup your raid groups and LUNs?
I mainly ask these questions because, while possible, we would rather not have to re-carve the disks at a later time because we goofed on the initial setup.
Any and all suggestions are greatly welcomed and appreciated. We are new to booting from SAN and best practices with regards to VMWare (we have been a growing ESX shop for the past year and a half, and plan to move this practice into a production environment later this year) and would like to hear some input/feedback.