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We have two hosts running VMWare ESXi 4.1. Both are connected to a RAID 5 array via iSCSI. We added three more disks to the RAID array. Now I need to assign the new storage somehow to the ESXi hosts. Right now we have one VMFS 3.46 datastore that consists of two LUNs on that array. Both ESXi hosts connect to that single datastore.

What would be the best way to add the new storage to the ESXi hosts? Should I just grow one of the LUNs to add the extra storage and then grow the VMFS? Or should I add about half of the extra storage to each LUN and grow the VMFS? Or should I create one (or two?) extra LUNs to add to the VMFS?

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If you are running out of space on the existig datastores and need the space for existing vms, expanding the current underlying luns and then VMFS may be the way to go.

If you are adding the space for new VMs, creating new luns and datastores may be a good path.

Are your current datastores close to the 2TB limit? Then you'll need to go the route of new datastores.

Do you have 'many' vms on your current datastores and does your array / licensing support VAAI? Lots of 'it depends' with these. If you have many vms with thin disks on the existing datastores and don't have VAAI, go the path of new luns and datastores to mitigate any locking issues.

How do you backup? Will expanding the current luns / datastores versus adding new impact your restore / backup windows or exposure risk in case of a VMFS issue?

Keep it simple, avoid extents, be aware of the maximums and limits.

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Well, considering the VMFS over ISCSI on RAID5, I don't think it makes a lot of huge difference from the performance perspective. It's all depends on your storage requirements.

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