how many hosts and luns in same datacenter ?

[EE99]

Hi,

I´m trying to find the best way to redesign a vi3 datacenter that have been growing a little to much without control.

Today it look lite this:

40 hosts, BL25

43 luns, 500G

>400 VM´s

All hosts can see all luns.

Hosts and VMs are grouped in TEST, PREPROD and PROD, but vmdk´s are spreed on all luns.

There is some performance issues and lot of scsi conflicts.

They also need to add 10 more hosts for 100 new vm´s that is going to be migrated from ESX 2.5.

I first plan to group luns in to TEST, PREPROD and PROD and then start to move all vmdk in to right place.

Then create 2 new farms and move in hosts. Then change the lun mask so that each farm only sees it´s own luns.

The PROD farm will than have 18-20 hosts and around 18 luns.

What is the recomendation on how many luns and hosts that can be in the same farm.

regards

[mreferre]

The rule of thumb I would say is clusters/farms comprised of 6-10 hosts a similar number of LUN's.

Of course this might vary depending on the storage requirements, how big your LUN's can be created etc etc etc.

Ideally you want to dedicate LUN's to prod / test etc etc if you can tier your storage (i.e. Raid10 LUN's for prod, Raid 5 LUN's for test etc etc). If you can't do that than I don't think it is a blasfemy to have equivalent LUN's and share them across the various environments (this will alleviate the problem of having high I/O vm's on production lun's and low I/O vm's for test ..... all would be averaged).

However there are many variables and it would be difficult to suggest something without knowing your environment. If I was to throw a number as I said I would probably create 5 clusters comprised of 8 hosts and 8 LUN's for your scenario.

But again ... it depends.

Massimo.

[VirtualNoitall]

Here is a good doc on maximum config specs: http://www.vmware.com/pdf/vi3_301_201_config_max.pdf

[Texiwill]

Hello,

Once you go over 8 hosts per LUN, expect SCSI reservation conflicts, yes some SANs can handle up to 16 hosts per LUN, but 8 is a very safe number. You may want to device your machines up into clusters for your different groups... Test, Prod, etc. That way you do not mix and match and things can be under better control.

In some cases I setup a deployment servers that can see every LUN. They are generally low powered boxes designed just for deployment of the VM and then the subsequent vMotion to the final home.

Best regards,

Edward

[VirtualNoitall]

There is more to SCSI reservation that just hosts. If you had 9 hosts and no virtual machines there would be no SCSI reservation issues. It has more to do with number of virtual machines and activities being performed. Based on this line of thinking no one would ever have a cluster of more than 8 nodes?

[mreferre]

I think that it depends.

If I get asked how fast one could usually go with a car my take is 40 miles per hour. Sure you can go 200 miles per hour if you are alone driving in a F1 circuit (which would be the "maximum" listed in that document) or 0 miles per hour if you are stuck in a traffic jam.

I guess it depends and every situation is different.

Massimo.

[Ub]

This all seems very finger in the wind type stuff,

Is there no way of extracting historical data on the number of reservations placed on a particular LUN from VC ?.

You could then start to understand what effects the reservations are having on the performance on each lun/host/vm

[EE99]

So I guess that I just have to test my plan and see if it works.

Even if there will be 20 hosts in one of the new farms, it will hopefullt work better than today.

When I split the datacenter, shuld I create new farms or just groupe the hosts in "san groups" and let them all stay in the same farm ?

[ChadAEG]

I believe there is a maximum of 16 physical hosts to a cluster/farm.

To see what kind of reservation conflicts your getting, you can monitor the wmkwarning log in /var/log for each of the hosts.