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 255 GB max memory limitation ? 
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Joined: Fri Sep 16, 2011 1:49 pm
Posts: 11
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Post 255 GB max memory limitation ?
Im using viclient to access ESXi 4.1 server and the Create a new VM gui provides a max memory size of 255 GB. Is this a really a limitation ? Perhaps using the ESXi fmkfstools cli would allow creating a larger VM ? I have not tried, but would be similar to:

vmkfstools -c 300G -a lsilogic VMname.vmdk

I have also found that when creating a 255G VM and installing RHEL6, the default partitioning provided for a VM with 8cpus and 55G ram is:

50G /
126G /dev/shm
485M /boot
83G /home

I realize that shared memory should be atleast 2x ram but I need atleast 200G for / since I have several large img partitions that the VMs will require. This concern is why Im asking about memory sizes > 255G since it appears that I need closer to 400G to support my architecture needs.

Any advice on creating VMs with greater than 255G is appreciated.


Fri Oct 21, 2011 5:24 am
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Joined: Mon Mar 16, 2009 10:13 pm
Posts: 3880
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Post Re: 255 GB max memory limitation ?
With ESXi 4.1 and lower the maximum size you can create for a virtual disk depends on the block size used to format the datastore. The default block size is 1 MB. You have options for
Block Size Max virtual disk file
1 MB 256 GB
2 512
4 1024
8 2048*

With ESXi 5.x this is no longer a concern as the default is 1 MB but you can go over 256 GB. With 4.1 and earlier the only way around this is to reformat the datastore. You can't change the block size otherwise.



* You'll want to max out at 2032 MB if you plan to use snapshots.

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Dave Mishchenko
VMware vExpert 2009-2013
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Now available - VMware ESXi: Planning, Implementation, and Security
Also available - vSphere Quick Start Guide


Fri Oct 21, 2011 6:09 am
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Joined: Fri Sep 16, 2011 1:49 pm
Posts: 11
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Post Re: 255 GB max memory limitation ?
Dave,

Thanks for this info on Block Size Max for the virtual disk file (vmdk)
Regarding the reformatting of the datastore you suggest if staying with the current ESXi 4.1 install, would this require re-installing the ESX. The current install has three (3) datastore's and not sure if one or all three would require the same block size ? I do not remember choosing this option when installing.

Are these topics covered in your book ?
I would like to review and have a Sarari account, can you provide a reference ?


Mon Oct 24, 2011 7:45 am
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Joined: Mon Mar 16, 2009 10:13 pm
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Post Re: 255 GB max memory limitation ?
The datastore created during the install defaults to 1 MB. When you create subsequent datastores it's an option, but easily missed.

I'm not sure I covered it in the book. The book intent was more geared towards migrating from ESX so a lot of the basic stuff wasn't covered.

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Dave Mishchenko
VMware vExpert 2009-2013
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Now available - VMware ESXi: Planning, Implementation, and Security
Also available - vSphere Quick Start Guide


Mon Oct 24, 2011 10:24 am
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Joined: Fri Sep 16, 2011 1:49 pm
Posts: 11
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Post Re: 255 GB max memory limitation ?
The default ESXi install create 3 datastore(s) for the 3 disk volumes on my system, 1 for a SATA HDD and the other 2 for the RAID5 volumes from 3 SAS HDD's.

I was able to convert 1 of the RAID5 datastore volumes using:
vmkfstools --createfs vmfs3 --blocksize 8M /vmfs/devices/disks/vml.02000000006782bcb051168400160f583c06cf0e35504552432036:4

It was not very clear how the /vmfs/volumes/datastore(s) mapped to the /vmfs/devices/disks/vml* and the viclient resource allocation did help to show the mapping of the datastore(s) to vmhbal:target:lun:hba volumes

I then relinked the datastore volume symbol:
/vmfs/volumes # ln -s 4ea6d5f6-b3fc8394-19fe-14feb5eaecc1 datastore3

Question:
I also notice the default ESXi install created 3 Hypervisor[123] links, should I also relink a Hypervisor ?

I was able to create a new VM on the newly formatted datastore3 and have a RHEL6 install running on this VM so not sure why the Hypervisor3 link is needed ?


Wed Oct 26, 2011 6:20 am
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