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Old 12-01-2008, 03:29 AM   #1
henryh3
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Smile Maximum addressable RAM in distros?


Hi,
I would like a little advice about which Linux distro to get.

What I want to do is run several VMware virtual machines (possibly a couple at the same time) on a Linux workstation, and use the workstation in it's Linux mode for non-windows (XP ond/or Vista) applications.

The hardware I am contemplating using is an AMD Athlon Dual core CPU and several Gb of RAM etc...

RedHat seemed to suggest that 256Gb was the max for their enterprise Linux, is this also the case for Fedora 10? (Not that I would be contemplating anything like this amount of RAM).

I would be thinking of 1Gb or 2Gb for each VM though.

What's the maximum addressable RAM for current distros and what are the suggestions for running VMs on Linux?

Thanks . . .
 
Old 12-01-2008, 03:53 AM   #2
thecarpy
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I think the only limit is hardware. Linux has no real limit on RAM size.
Linux can even overcome 32bit hardware limitations (3.4Gb), and you are using a 64bit CPU ... ;-) I do not think this is distribution-dependent, either!

At work, we have linux workstations (not servers) running ubuntu with 8Gb of RAM ... no probs, what were you considering?

We also have a few systems running Suse enterprise with 16Gb of Ram or more ... Suse enteprise because of the legacy ...
 
Old 12-01-2008, 04:21 AM   #3
henryh3
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Quote:
Originally Posted by thecarpy View Post
At work, we have linux workstations (not servers) running ubuntu with 8Gb of RAM ... no probs, what were you considering?

We also have a few systems running Suse enterprise with 16Gb of Ram or more ... Suse enteprise because of the legacy ...
I was thinking of Fedora 10 (or possibly Ununtu), I can't seem to get my head around Suse.

Do you have a preference and/or suggestion as to what may support VMware best? (Is it actually bundled with any of the distros?

I'm really pretty open WRT the flavour of Linux as I haven't really used any of them much, or enough to become enamoured with one at the expense of the others.

Thanks for the opinion about Linux being able to handle an undefined amount of RAM.

Henry.
 
Old 12-01-2008, 04:58 AM   #4
thecarpy
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It is obviously not infinite, but well above anything any of todays hardware can cope with, so what is the point ... theoretically, i think it is in exabytes, but theory and practice are two separate things.

Just like 32bit systems can cope with 4GB of ram in theory, in reality it is closer to 3 GB, because address space is not only used for ram ... etc etc etc ... and linux can cope with 16GB or 64GB, cannot remember, on 32 bit platform, with a hack ... but applications do not like that, especially drivers, and may crash frequently.

We have a gsx server, and that is why we went for enterprise Suse. Vmware only supported redhat and suse (enterprise editions) at the time and nobody in their right mind would use Redhat ;-) ... I also strongly discourage from using Suse ;-), although I started with Suse and had been a longtime Suse user ...

Go for ubuntu x64, get vmware workstation, which costs you money, but it works very well on linux/ubuntu, and have fun!!!

Remember, when you buy RAM: quality is always more important than quantity!!! In other words, instead of getting 4 dimms of RAM immediately, just get 2 of the best quality you can afford and see how it goes.
 
Old 12-01-2008, 07:05 AM   #5
salasi
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Quote:
Originally Posted by henryh3 View Post
The hardware I am contemplating using is an AMD Athlon Dual core CPU and several Gb of RAM etc...
The 'hack' (greater than 4g adress space on a 32 bit kernel) is hardware dependant; I know more about Intel than AMD, but if you are buying hardware specially for this, then you need to check whether the chipset is compatible (my feeling is that most modern chipsets will be, but I don't know). And anyway, the 'hack' doesn't give an indicidual process access to >4G; how this works out with several VMs I'm not sure, but you may well think that the hack is worth avoiding and that the real 64 bit version is what you want.

As far as the 64 bit kernel is comcerned, its a 64 bit kernel; I don't know of any differences between distros in the adressing range of their 64 bit kernels. They all get it from the same place, they apply a few (unfortunately, quite a few) patches, but I don't know that anyone restricts the address range.

What you do have to look out for is that a 64 bit kernel is available; this will be true of all of the biggies (RH, SuSE, debian) but may not be true of the compact or special purpose ditros (Puppy, DSL, security audit distros, live distros), but you shouldn't be considering one of those, anyway, for what you want.
 
Old 12-01-2008, 02:38 PM   #6
estabroo
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I believe most linux x86_64 kernels are limited to 64GB because I believe they only use 36 bits of address space for physical memory, (I could easily be wrong).
 
Old 12-01-2008, 03:25 PM   #7
syg00
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Nope - that's a rough description of PAE. For 32-bit hardware. The kernel supports this extra RAM by utilising those extra address lines - as mentioned, individual processes are still limited to 4 Gig virtual addressing range.
Irrelevant for 64 bit.
 
Old 12-01-2008, 03:54 PM   #8
lazlow
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You might want to keep in mind that Fedora only supports any one release for about 13 months. After that 13 months(EOl)(End Of Life) there are no updates of any kind.

What you may want to consider is Centos. Centos is RHEL (Red Hat Enterprise Linux) with the logos stripped out. It is binary compatible with RHEL and has a five year(+) support life. It is free to download and update (unlike RHEL).

As the others have hinted at, for machines with less than 3gb ram use 32bit, for machines with more use 64bit(regardless of distro).
 
Old 12-01-2008, 05:36 PM   #9
henryh3
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Cool Thanks for the clarification & advice! :-))

Centos looks like the best option from what has been said.

I will be using a 64bit CPU and consequently a 64bit version so that should preclude me from having to think about hacking and the possible problems associated with this.

So far as I am concerned (at the moment and for the foreseeable future -2 years-) 64Gb of RAM will more than suffice for my needs.

(As an aside, it seems bizarre to me that I am thinking in terms of 10s of Gb of RAM, when I can remember configuring a -high performance- workstation with 100Mb HDD and 1Mb of RAM)!

Thanks for all your knowledge and ideas . . .
 
  


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