Hosts per LUN

[AllBlack]

Hi everyone,

I have never really thought about this until I started going through some of the design books that are out there.

All this is based on what I read in there.

It is suggested to stick to a dozen or so hosts per cluster and you should connect no more than 8 hosts to a single LUN.

If I follow this guideline, what is best practice as to which 8 hosts I decide to connect to a given LUN?

What about DRS/HA in such a cluster? Is DRS and HA smart enough to figure out that a certain host has no access to a certain LUN

and pick another host or would it just fail?

Does this question make sense?

Cheers

[Rodos]

The real question is cluster sizing, how many hosts should you put in your cluster. There will be many considerations of this, including storage scaling as you have mentioned, because the more hosts in the cluster the more that have access to a particular LUN.

Its not really a good idea to break the VMotion boundary within the cluster by zoning LUNs to only certain hosts. VMotion are smart enough to not move the machine to a host that does not have access to the LUN but your management overhead will drive you crazy. Don't do it.

Just connect the LUNs to all 12 hosts. You will have much bigger issues to deal with in a cluster that size.

Rodos

Consider the use of the helpful or correct buttons to award points. Blog: http://rodos.haywood.org/

[Texiwill]

Hello,

The real question is what your SAN/NAS will support. If it supports 12 hosts per LUN go for it. If it only supports 4 hosts per LUN, consider making 3 clusters. For example a MSA1000 could only handle 4 hosts per LUN before things went screwy.... Some other SANs could handle 16 hosts per LUn and still others could only handle 8 hosts per LUN...... It really depends on the hardware you are using more than anything else as well as what the VMs are doing and what you are doing to the VMs.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education.

Blue Gears and SearchVMware Pro Blogs: http://www.astroarch.com/wiki/index.php/Blog_Roll

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[AllBlack]

Thanks guys,

As I am only thinking of putting 10 hosts per cluster I would not see any issues with going for that number per LUN.

Thanks for pointing out the SAN limitations! It is something I did not even consider!

We are using different SANs (Clariion cx3-20 & MSA2000) so I will start looking into that.

cheers

[Texiwill · Accepted solution]

Hello,

The clarion should have no problems but the MSA2000 may have some. I have not done much research on it. The easiest way would be to add hosts to LUNs until SCSI REservation Conflicts arise.... That will give the upper limit.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education.

Blue Gears and SearchVMware Pro Blogs: http://www.astroarch.com/wiki/index.php/Blog_Roll

Top Virtualization Security Links: http://www.astroarch.com/wiki/index.php/Top_Virtualization_Security_Links

[JonRoderick]

Hi

any idea on the host/LUN limitations of IBM's DS8x00 and SVC?

Cheers

Jon

[Texiwill]

Hello,

I would say minimally 8. THe way to find out is to run loads on your ESX hosts and keep adding hosts with the same load until SCSI Reservation requests start happening when you are not physically doing anything but running VMs. I.e. no VMotion/SVMotion/management of any kind.

ESX is never really idle with the respect to SCSI reservations but if your nodes all have similar loads you can then judge when things will start to break just by adding hosts.

The data in VMware ESX Server in the Enterprise came from doing that.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education.

Blue Gears and SearchVMware Pro Blogs: http://www.astroarch.com/wiki/index.php/Blog_Roll

Top Virtualization Security Links: http://www.astroarch.com/wiki/index.php/Top_Virtualization_Security_Links

[JonRoderick]

Thanks, you mean a minimum of 8 (so room for more)?

Jon

[Texiwill]

Hello,

Any number up to 8 without testing. After 8 I would start some testing.... You could probably go much higher but it is best to look for errors, etc. as you go forward.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education.

Blue Gears and SearchVMware Pro Blogs: http://www.astroarch.com/wiki/index.php/Blog_Roll

Top Virtualization Security Links: http://www.astroarch.com/wiki/index.php/Top_Virtualization_Security_Links