[Pvfs2-developers] host id

[Walter Ligon]

Where I think I'm going it to store the Handle of the "owner" of each 
object as an attribute in the object.  For dfiles, this would be the 
handle of the metafile, for metafiles this would be the handle of the 
directory (works for now since we don't do hard links).  Then We'll send 
reference the owner handle when we create the capability.  This would be 
translated into a server name, and we tie the key pairs to the servers. 
  Thus, if we change which server handles a data space, the owner object 
handle will translate to the new server, and it will use that server's 
keys.  The allocating and management of keys will be tied to the 
servers.  this should even allow migration of objects between data 
spaces.  If data is migrated to new servers, probably the new servers 
will each get new keys.  We plan to have a mechanism to flush and 
rebuild key databases for this eventuality (basically we can request 
public keys from a server with a PVFS request - they keys are sent in a 
cert signed by CA).  Finally, having this information added might be uf 
use to the fsck program, as it would allow stray dfiles to be mapped 
back to the owning metafile, etc.  The only problem would come if we 
actually change the handle of a file, which would require updating all 
of the dfiles - but we don't do that very often.

Thoughts?

Walt

Sam Lang wrote:
> 
> Walt,
> 
> I think for your purposes you should probably just have each server/fs 
> generate a uuid.  Keep in mind that everything (including the endpoint 
> string and handle ranges) can change in the config file without 
> recreating the storage spaces.  This often happens when admins want to 
> migrate to other servers.
> 
> It might help to think about the storage space (and each fs within them) 
> as the thing you want to reference with a permanent globally unique-id.  
> Our servers just manage those storage spaces, and the endpoint strings 
> just provide an address (which can change over time).
> 
> If you were to use a uuid for each server/fs, you probably want random 
> instead of time/host-based, so that you can move servers around without 
> making the id invalid.  If you wanted them in the config file, they 
> could be part of the Alias mapping, and genconfig could just generate 
> them with uuidgen or something.  We've talked about having something 
> like this for zero-conf, although that was more transient on a 
> per-server start basis, to provide a consistent view if the config 
> changed -- so a different purpose.
> 
> Alternatively, if that's all too over the top, and you just want an 
> integer instead of a string, the index into the server list is no worse 
> than the endpoint string.
> 
> -sam
> 
> 
> On May 15, 2008, at 1:23 PM, Rob Ross wrote:
> 
>> Yes, having multiple file systems would really mess with you because 
>> you could have the same handle for more than one FS. You sure you 
>> don't want to just use a string name?
>>
>> Rob
>>
>> On May 15, 2008, at 1:10 PM, Nicholas Mills wrote:
>>> Thanks for your help everyone.
>>>
>>> David and I have decided to use the first handle in the server's 
>>> mapping to identify the server. We are at the point now where we need 
>>> to find a handle range given a host alias. Does anyone know of a 
>>> quick and easy way to do this?
>>>
>>> There is also the question of which handle range to use. Do we use 
>>> the meta handles or the data handles? Also, will having multiple 
>>> filesystems complicate anything?
>>>
>>> --Nick
>>>
>>> On Tue, May 13, 2008 at 4:10 PM, Phil Carns <carns at mcs.anl.gov> wrote:
>>> I don't think we have any globally valid fixed sized identifier for 
>>> the servers.  The only option I know if would be to use a handle (for 
>>> example, the first handle in the server's mapping) to represent each 
>>> server.  I think just using the string name would be safer, though.
>>>
>>> -Phil
>>>
>>>
>>> Walter Ligon wrote:
>>> Hey guys,
>>>
>>> we're needing to send a server host identification on the wire.  In 
>>> the config the host_id appears to be a variable length string.  
>>> Should we just use that, or is there something else of fixed size I'm 
>>> not aware of?
>>>
>>> Walt
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