Multiple LUNS in VMWare with iSCSI

Hi All,

I am running a PS4000XV in an VMware vSphere 4 environment. I do have multi pathing setup and configured as per Dells recommendations. I have a question related to performance, I know I can have up to around 10 VM's in VMFS datastore however, this really does limit the number of paths I have to SAN. I have 3 NIC's dedicated to multipathing so if I have two LUNs setup on the iSCSI SAN I have a total of 6 paths for active IO to the SAN.

Should I use a LUN for every 2 VM's for instance? Or should I use just one big lun? WHat are you thoughts on this and will using more LUNs give me more paths therefore greater potential for performance gains during heavy IO.

If I use 1 big lun

Total Paths: 3 per ESX Host

4 LUNs

Total Paths: 12 per ESX Host.
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vmwarun - ArunCommented:
Even when you have multiple paths to a LUN, the ESX Host can only use one path at a time.
Multipathing is configured so that in case of failure of a single path, an alternative path can be used.
The number of VMs which you can have on a LUN is with respect to the type (Web, DB or Application) of servers in that particular LUN.
For example, Web Servers are NIC Intensive while DB Servers are Disk Intensive.
Plan your reqirementrs

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vmwarun - ArunCommented:
*Plan your requirements and size your LUNs accordingly.
Regarding your LUNs design, I would recommend a 3 LUN minimum :
-1 based on a RAID 1/10 array for OS/Swap/Temp/Logs needs
-1 based on a RAID 1/10 array for Databases Data&Index usages (random io intensive as for Databases, EMails, Office FileServers)
-1 based on a RAID 5/6/50/60 (stripe = 1MB for Win2008) array for Backup/Archive/WriteOnceReadMany usages (Backup, Archive, Media, Low accessed FileServer, most Web servers, Print servers)

Now, you may although add some dedicated LUN to isolate a critical app
Although sizing those LUN to define how many drives are to be put in each array is not easy and requires a lot of work to identify expected IOPS usage per VM. Remember SSD/EFD rules this IOPS world (To sustain the same IOPS needs, you can replace 13x SAS 15k HDD by 1 single X25-E SSD)
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