vmfs or raw for vms? which to choose

[ranjitcool]

Hey Guys,

We have a EMC SAN and talks to esx host over iscsi. Now when i carve a new lun lets say lun1 of 100gb, shud i present it to its designated vm as a vmfs datastore or raw? which is better also wud vmotion work on both?

please assist. I think if i have it as vmfs then the 100gb lun can be used by different OS's and can be shared, this is going to be a critical server so is that a good way?

please advice

thanks

rj

May be we all live virtual lives..

[vm_arch]

Firstly what will be going into the LUN (i.e email database, User files, applications...)

Secondly; for vMotion to have a hope of working you have to present that LUN to all of your ESX servers and only to one VM.

Thirdly, a VMFS partition is just a storage container for virtual disks. You can create multiple virtual disks inside a VMFS (and multiple VMs can have virtual disks inside one VMFS, but the VMFS is only 'accessible' to one OS - that being the VMWare ESX server. The Virtual machines that have virtual disks inside that VMFS can be of entirely different OSes, as they dont see the vmfs... they simply see the virtual disk that is created IN the vmfs.

My suggestion:

I only use Raw Device Mappings for stuff like large file and print or database LUNs - never for something at or under 100Gb (usually for 1/2Tb or larger). If you want to have several VMs using smaller disks (like say 4 vms with 20gb disks) then a 100Gb VMFS partition would be perfect for that.

Hope that clears it up

[ranjitcool]

Well the luns hold sharepoint servers including the database.

I think your explanation regarding how vmfs is accessed makes a little sense now. I did know of how it is accessed and seen by different vms but if I have a database on a vmfs lun, then performance might be affected since too many vms access the same vmfs? (correct me if i am wrong)

Do vmfs lun and a raw lun work with vmotion? or does any one of those DONT?

Thanks

RJ

May be we all live virtual lives..

[mreferre]

if I have a database on a vmfs lun, then performance might be affected since too many vms access the same vmfs? (correct me if i am wrong)

Remember that your raw device would be a LUN carved out from an array that will support more LUNs anyway. So your DB (even on a RDM) would have to fight for contention for disk access (disk = actual physical spindle) among other VMs (on VMFS or RDM on the same array). This is unless you dedicate each LUN an array (which doesn't make sense at all).

All in all it's a trade-off between performance and manageability. And since RDMs have never showed HUGE perf improvements Vs VMFS/VMDKs it's a no brainer (generally speaking).

Massimo.