db servers separate hardware

[Paul Blackburn]

Patty,

In my experience, the issues to consider are:

a) Do we want to provide users with optimum service from the db servers?
    If yes, then it makes good practical sense to run pure database servers

    running nothing else that may degradate performance.
    All surplus processing removed leaves more compute cycles for db
service.

b) Do we want to provide optimum availibilty/reliability for the cell?
    If yes, then splitting out the function is a good thing (tm).

    We don't want to carry all our eggs in one basket.
    We do want to use machines of appropriate size and capacity
     for their function. For fileservers: plenty of disk space and high
speed
     network connectivity ideally located "close" to users (on the
network).
     For database servers: just enough disk and RAM.

c) Do we want to provide minimum downtime from system upgrades
    and system maintenance?
    If yes, then we should not consolidate onto fewer servers rather
    we should ensure we have enough spare capacity to have perhaps
    a "hot standby" db server and fileserver. This allows for a
    "rolling upgrade": taking one server out for upgrade without
    breaking the service.

d) There is the general "KISS" principal or Keep It Simple Stupid! ;-)
    The more complexity we load on a machine the greater the probably
    of problems. When you upgrade package "a" does that have
    a knock-on effect on package "b"? Will you need to reboot
    to apply a kernel fix for package "z".

e) To improve performance and distribute load it is better to have
    more servers not less.

f) If a server crashes, what is the impact on users?
   Consider the case of a cell with 3 db servers and 4 fileservers.
   If one of the three db servers crashes the cell continues
   to run with minimum degradation: all files continue to be served.
   Clearly this is not the case if db and fileserver function is on one
machine.

However, I guess the bottom line is cost. How many servers can you afford?
What kind of AFS service are your users expecting?

I hope this helps.
--
cheers
paul                       http://acm.org/~mpb

Patty OReilly wrote:

> Management wants to consolidate services where possible at our site. We
> have always adhered to the recommended practice of keeping our Database
> servers running vlserver, kaserver, ptserver and buserver on separate
> machines from our Fileservers. Now they want us to consolidate these
> services and run all AFS server processes on our Fileservers.
>
> Does anyone have any information pro or con that could help us decide
> whether consolidation of Fileservers and DBservers would be successful?
>
> --patty