This afternoon @Stevie_chambers published something on twitter on memory limits of vSphere VMs. This was a recap of a question asked on a VMware internal mailinglist, here’s what Steve posted:
Why has a vSphere VM max mem 255GB? VMFS block size of 1MB = 256GB max – 0.4MB VM state = 255.6MB rounded down to 255GB – from Ole@VMware
In other words, the maximum memory size for a vSphere VM is 255 GB. This is the maximum memory size because a swap file needs to be created as well. This swap file cannot exceed the maximum file size of a 1MB blocksized VMFS volume. Max file size = 256GB – VM state(roughly 400MB)=255.6GB. For safety this has been rounded down to 255GB. Which at first sounds like a weird amount but actually makes sense when you read the explanation.
By the way, Steve has recently started a blog: View Yonder. Welcome to the blogosphere!
Hi Duncan,
Very instructive but what about bigger block size ?
Bigger block size or not, the limit is still 255GB for the same reason. It’s a safety limit.
But the file size limit increase with the block size so it could be more right ?