Configure addition HDD on VMware server

My current VMware has 4 HDD running in RAID-5, with one datastore on the VM server.

I will add 4 more HDD to the server. Just wonder whether there is any difference in performance if

1. configure 4 new HDDs with separate RAID5 with a new datastore
2. extend the current RAID with "4 HDDs"  and extended the size of the existing datastore.

Any comment ? Tks
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
More Spindles = More Disks = More Performance = More IOPS.

So yes, the more spindles in a RAID set, will give your VMs more IOPS.

Some Rough calculations...

RAID with 4 Disks

RAID 5 4 x 600 SAS 15k Drives - Approx 200 IOPS each disk. assuming 33% writes

Total IOPS = (200 IOPS x 4 disks)/(0.67+4*.33))
           = 402 IOPS

RAID with 8 Disks

RAID 5 8 x 600 SAS 15k Drives - Approx 200 IOPS each disk. assuming 33% writes

Total IOPS = (200 IOPS x 8 disks)/(0.67+4*.33))
           = 804 IOPS

So a difference of 400 IOPS, e.g. DOUBLE the IOPS!
Scott GorcesterCTOCommented:
I don't think you will have a noticeable difference in performance. If you are going to add the drives to the existing RAID 5 make certain that the speed of the drives is identical. Also the drives cannot be smaller in capacity and if they are larger capacity the extra space will not be accessible. Adding drives to the array may improve the performance of the array due to having more spindles.

#Edited By

Andrew Hancock
VMware Zone Advisor
Scott GorcesterCTOCommented:
ok ty
AXISHKAuthor Commented:
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