[OpenAFS] how?: Distribute /home to n Terminal Servers

[Steve Wright]

Nathan Rawling wrote:

>Steve,
>
>>>*every* machine that wants to access files that live in /afs needs to
>>>be an afs client.  This includes AFS server machines.
>>>
>>ok.  Since we have a small number of machines, what would be the
>>situation running *all* (max 10) machines as AFS Servers, and then
>>acting as their own clients,
>>
>
>My understanding is that you want to keep the number of DB servers down
>because of performance issues when you have too many. I suspect that
>probably three DB servers would be sufficient for your application. You
>want more than one to eliminate your risk of a single point of failure,
>two is not recommended for technical reasons, so three is a good bet.
>

Thanks for that Nathan.

Are the 'performance issues' ethernet related, or processor related ? 
 We can easily place this traffic on a private network segment.


>
>With that said, you could run the file server portion on each of your
>terminal servers if you so desire. If your prime goal is to distribute
>load, that might be the way to go.
>

The prime goal is redundancy and simplicity.  I understand AFS is lots 
more complex than an NFS solution, but we can mostly package the system 
pre-configured, and the hardware/networking pre-specified.


>>ok.  Will the clients still sync if the server is down ?  Will we still
>>have our single point of failure ?  Can more, or all of the Terminal
>>Servers act as OpenAFS Servers, as well as a client for the cell ?  Can
>>we then `mount` this cell as /home ?
>>
>
>Well, with one server, you would definitely have a single point of
>failure. As Dan Pritts mentioned, even with a multiple server solution as
>I talk about above, a server outage would result in some user home
>directories becoming unavailable.
>
>As you spread the user volumes across more fileservers, you reduce the
>impact of the loss of one of them. If you use every one of your terminal
>servers as a file server, and you have 10 servers, you only lose 10% of
>your user volumes if/when a server dies.
>

Ok.  I would have mounted /home/ as *one* volume..  Can we have each 
server maintain it's own sync'ed (cached) copy of the same (/home/) 
fileset ?

I only need all the directories under /home/


>
>I have heard that Netapp has an implementation of NFS with working
>read-write failover, and I know that Veritas has a solution. However, I'm
>sure that either would charge big bucks.
>

eeeh, ah well.


>>We simply want 2-10 Terminal/Application Servers that keep /home/* +
>>UIDs + GIDs sync'ed at all times.  All these Terminal/App Servers are on
>>the same physical Ethernet Segment, firewalled in, on one site, and
>>probably in the same rack - although it would be nice to distribute
>>across the complex/campus near their associated set of Terminals.
>>
>
>You should watch out for the technical limitations of AFS as a solution.
>If you have users with files larger than 2gig, AFS is not probably the
>best solution. 
>

2 gig ?  shivers..  there would be no hdd space left !   nah, seriously, 
1 700MB CD ISO at the most..

>Byte-range file locking is another common area of concern.
>

I'm not up on that at this stage..  I trust I can safely ignore it for 
now ? (famous last words...)

>
>The largest administration hassle with AFS, in my experience, has been
>managing the backups. The bundled backup system is cumbersome (although it
>has probably been greatly improved since I last used it), so frequently
>you have to work out a solution that matches your environment.
>

<shrug>  Why can't I just `init 3 && cp -a /home /somewhere/else && init 
5`  ??

Sorry if that's an ignorant question, but it seems logical to me..

<spacer between questions>

 I *thought* I heard that there is no such thing as UIDS + GIDS on an 
AFS filesystem ?   (I expect I'm really showing my ignorance now..)



Thank you people.  Please, anything that anyone would like to add, feel 
free...

regards,
Steve