Maximum # of ESX hosts mapped to a single LUN

[JFritsch]

I have a 1.9TB LUN presented from an IBM SVC to several ESX/ESXi clusters which include versions 3.5(ESX), 4.1(ESXi) and 5.0(ESXi).  I read that 3.5 has a 32 Host to LUN "recommended" limit.

I'm looking for more detail about this number.  Does this apply only to the number of 3.5 hosts that can see the datastore or all ESX hosts combined.  And why is it recommended vs a hard limit?  We're trying to set up one LUN mapped to as many ESX clusters/hosts as we can in order to support a mass migration to a new environment.

I'm pretty new to the VMWare world so please excuse me if I'm not clear about what I'm asking or have not included other pertinent information.

[RParker]

JFritsch wrote:

I'm looking for more detail about this number.  Does this apply only to the number of 3.5 hosts that can see the datastore or all ESX hosts combined.  And why is it recommended vs a hard limit?  We're trying to set up one LUN mapped to as many ESX clusters/hosts as we can in order to support a mass migration to a new environment.

It's not a SAN limitation it's an ESX limitation by cluster.  Technically 3.5 cannot share data with ESX 5.0 hosts, because the VMFS will not be compatible... unless you use existing VMFS with ESX 5.0 hosts..

But the limit is for ESX, so since you have mix of 3.5 and 5.0, then the limit is because of the VMFS version, 32 3.5 hosts is the limit, 256 ESX 5.0 is the limit, 3.5 cannot share more than 32.

I would NOT recommend sharing a LUN with 3.5 and 5.0 for that reason.  Keep LUN separate.  Upgrade your hosts to 5.0 and use that LUN at its 256 connection limit.

It is a hard limit, the "recommendation" should read VM Ware recommends a LIMIT of 32 connections (MAX connections).  They are certainly not suggesting you connect 32 hosts just because. . .  .

http://www.vmware.com/pdf/vsphere5/r50/vsphere-50-configuration-maximums.pdf

[mcowger]

Parker - where are you seeing 256?  On that page I'm seeing a limit of 64 hosts connected to a volume, not 256.

[TomHowarth]

Matt,

It is in table 4 of that document,

Physical iSCSI Targets 256

Software iSCSI Targets 256

NFS Mounts per host 256

LUNs per Host 256

However the maximum LUNIDs is 255 (but you can assign a LUNID of 0)

VMFS5 Volumes per host 256

however Hosts per Volume is 64

that is a contradiction.  I would like clarified.

[mcowger · Accepted solution]

I dont think its a contradiction at all.

It says a given host can have up to 256 LUNs.  A given volume (VMFS) can be accessed by up to 64 hosts.

They are 2 totally different scenarios.

[TomHowarth]

So then Richard is right the maximum number of LUNs a host can address is 256

[mcowger]

He is, but thats not the question the OP asked.

The OP asked how many hosts can be mapped to a given LUN, which this document would suggest is 64.

[JFritsch]

Somewhat confusing based on the way you look at it but mcgower summed it up nicely and provided the answer I was looking for.  Thanks to everyone for weighing in.