32gb ddr3

[pcslookout]

Would 32 GB of DDR be worth it if you like running Virtual Machines ? Does it depend on how many ? What would be the maximum limit with 32 GB before your processor would get overloaded as well. Lets say you have a pretty up to date processor. The latest i7.

 

[imagoon]

Depends entirely on the the VM needs. I have run 96GB RAM with 15 VM's on one single 2.40 Quad Xeon. Due to the nature of most of the machines I was never CPU constrained.

 

[heymrdj]

Would 32 GB of DDR be worth it if you like running Virtual Machines ? Does it depend on how many ? What would be the maximum limit with 32 GB before your processor would get overloaded as well. Lets say you have a pretty up to date processor. The latest i7.

It is very much worth it if you have several VMs. I like to give most VMs at least 2 GB of ram, so if I'm running VMWare Workstation 8 in Windows 7 that gives me approx 28GB of RAM to give VM's, or about 14-16 VM's. If you're using a baremetal hypervisor such as ESXi or XenServer, then that frees up a bit more ram towards VM usage.

Now in reality it really does depend on what VM's your're running. A virtualized SBS 2011 OS needs about 12-16GB of RAM all by itself, same for a virtualized fully loaded email processor such as Zimbra or Exchange. Apps like these spike processor usage, but remain relatively idle, enough so that the few peak times wouldn't really warrant using more than your standard high end i7 (cost efficiency). But you'll still need all that RAM.

 

[pcslookout]

Thanks never realized one Virtual Machine could take up so much ram.

 

[lsv]

Thanks never realized one Virtual Machine could take up so much ram.

2gigs a pop seems about right, they're complete sessions right

 

[heymrdj]

2gigs a pop seems about right, they're complete sessions right

Pretty much, you always want to provision a VM as if it was running on a box by itself (IE Windows 7 runs on 1GB of RAM, but it's not fun at all, 2GB is highly recommended, 4GB if you can). Same goes for SBS 2011, by all means it will run on 6GB of RAM, but it is so slow you'll be pulling your hair out, boots can take as long as 30-45minutes from a RAID 5 array. 12GB is really the minimum for it. On top of that I try to over-provision ram on VM's versus physical machines, because of the excess steps required for the VM's to reach disk I/O making it not perform quite as well as the real thing. I want everything to run in RAM as much as possible.

 

[pcslookout]

2gigs a pop seems about right, they're complete sessions right

I am talking about the actual virtual machines using all of the ram you allotted to it. Not the amount of ram the virtual machine software uses for it.

 

[pcslookout]

Pretty much, you always want to provision a VM as if it was running on a box by itself (IE Windows 7 runs on 1GB of RAM, but it's not fun at all, 2GB is highly recommended, 4GB if you can). Same goes for SBS 2011, by all means it will run on 6GB of RAM, but it is so slow you'll be pulling your hair out, boots can take as long as 30-45minutes from a RAID 5 array. 12GB is really the minimum for it. On top of that I try to over-provision ram on VM's versus physical machines, because of the excess steps required for the VM's to reach disk I/O making it not perform quite as well as the real thing. I want everything to run in RAM as much as possible.

Good point I guess the ultimate way to run a lot of virtual machines the fastest way possible is have like 64 GB of ram and install them all on a 32 GB ram drive?

 

[heymrdj]

I am talking about the actual virtual machines using all of the ram you allotted to it. Not the amount of ram the virtual machine software uses for it.

That's a growth that has to be carefully monitored for cost ratio importance. Windows 7 VM's will gladly keep pulling more RAM as you give them more up to say 4GB. At 2GB it will boot up to about 1.7GB because of prefetch, give it 3, and it'll boot to 2.25, give it 4 and it'll boot to about 2.5GB or so all because of Prefetch. Windows 7 can get by with less, especially if you're just testing with the VM. But if these are going to be thin provisioned desktops for actual usage by people you would want to give each VM 4GB of RAM. Safely, depending on app usage in the VM, you could then get away with maybe 125-130% over provisioning (giving the sum of the VM's more RAM than the server physically has based on the fact not all VM's need all their RAM at once).

 

[heymrdj]

Good point I guess the ultimate way to run a lot of virtual machines the fastest way possible is have like 64 GB of ram and install them all on a 32 GB ram drive?

Using enterprise SSD's for the datastore seems to be the in thing these days. It's extremely expensive though (about 2,000$ for 300GB storage, 6,000$ for 1TB). Only the most important I/O sensitive VM systems get placed on these kinds of datastores. Other than that cheaper RAM and slower disks are the choice, and you deal with the latency.

As to using a RAMDisk, that's discouraged. RAMDisks are volatile (can't withstand a complete power loss, and lose all data if power is removed). Therefore storing 400GB of a irreplaceable database (other than backups which are excruciatingly slow) onto a volatile storage array is not highly recommended