[Beowulf] Compute Node OS on Local Disk vs. Ram Disk

Jon Tegner tegner at nada.kth.se
Wed Oct 1 15:09:39 EDT 2008


There seem to be significant advantages using Scyld ClusterWare, I did 
try it (Scyld?) many years ago (when it was free?) and I was impressed then.

However, when looking at penguincomputing.com I don't find any price 
quotes. It seems - unless I miss something - one has to fill in a rather 
lengthy form in order to get that information?

In order to consider the "Scyld solution" I think it would be good to 
have at least an estimate of the price?

Regards,

/jon

Donald Becker wrote:
> On Wed, 1 Oct 2008, Bogdan Costescu wrote:
>
>   
>> On Tue, 30 Sep 2008, Donald Becker wrote:
>>     
>>> Ahhh, your first flawed assumption.
>>> You believe that the OS needs to be statically provisioned to the nodes.
>>> That is incorrect.
>>>       
>> Well, you also make the flawed assumption that the best technical 
>> solutions are always preferred. From my position I have seen many 
>>     
> ...
>   
>> a solution like Scyld's limits the whole cluster to running one 
>> distribution (please correct me if I'm wrong), while a solution with 
>> node "images" allows mixing Linux distributions at will.
>>     
>
> That's correct.  Our model is that a "cluster" is a single system -- and a 
> single install.
>
> That's for a good reason: To keep the simplicity and consistency of 
> managing a single installation, you pretty much can have... only a single 
> installation.
>
> There is quite a bit of flexibility.  The system automatically detects the 
> hardware and loads the correct kernel modules.  Nodes can be specialized, 
> including mounting different file systems and running different start-up 
> scripts.  But the bottom line is that to make the assertion that remote 
> processes will run the same as local processes, they have to be running 
> pretty much the same system.
>
> If you are running different distributions on nodes, you discard many of 
> the opportunities of running a cluster.  More importantly, it's much 
> more knowledge- and labor-intensive to maintain the cluster while 
> guaranteeing consistency.
>
>   
>>> The only times that it is asked to do something new (boot, accept a 
>>> new process) it's communicating with a fully installed, up-to-date 
>>> master node.  It has, at least temporarily, complete access to a 
>>> reference install.
>>>       
>> I think that this is another assumption that holds true for the Scyld 
>> system, but there are situations where this is not true.
>>     
>
> Yes, there are scenarios where you want a different model.  But "connected
> during important events" is true for most clusters.  We discard the
> ability for a node to boot and run independently in order to get the
> advantages of zero-install, zero-config consistent compute nodes.
>
>   
>>> If you design a cluster system that installs on a local disk, it's 
>>> very difficult to adapt it to diskless blades.  If you design a 
>>> system that is as efficient without disks, it's trivial to 
>>> optionally mount disks for caching, temporary files or application 
>>> I/O.
>>>       
>> If you design a system that is flexible enough to allow you to use 
>> either diskless or diskfull installs, what do you have to loose ?
>>     
>
> In theory that sounds good.  But historically changing disk-based
> installations to work on diskless machines has been very difficult, and
> the results unsatisfactory. Disk-based installations want to do selective
> installation based on the hardware present, and write/modify many links
> and configuration files on installation -- many more than they "need" to.
>
>   
>> The same node "image" can be used in several ways:
>> - copied to the local disk and booted from there (where the copying
>> could be done as a separate operation followed by a reboot or it can
>> be done from initrd)
>> - used over NFS-root
>> - used as a ramdisk, provided that the node "image" is small enough   
>>     
>
> While memory follows the price-down capacity-up curve, we aren't quite to
> the point where holding a full OS distribution in memory is negligible.
> Most distributions (all the commercially interesting ones) are
> workstation-oriented, and the trade-off is "disk is under $1/GB, so we
> will install everything".  It's foreseeable that holding an 8GB install 
> image in memory will be trivial, but that will be a few years in the 
> future, not today.  And we will need better VM and PTE management to make 
> it efficient.
>
>
>   

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