Samuel Douglas wrote:
On Sat, Apr 19, 2008 at 5:54 AM, Reinis Rozitis <r@xxxxxxx> wrote:
That way the afr-copying is done on the "server" level..
Only drawback in this is your clients can mount only one server so if one
goes down you have to remount or implement some other HA method (like dns or
heartbeats)).
This is a fairly serious drawback, but it depends what you want AFR
for. In our cluster system, we are probably using AFR with two
children to provide file replication; until the HA translator is
available, these are loaded on the client.
I'm not sure that it is that big a drawback. Using HA or RHCS to fail
over the IP resources sounds like a pretty standard way to implement
fail-over. The major drawback is lack of explicit load-balancing, but
having said that, if you mount by hostname you'd still get round-robin
DNS load balancing, which is probably good enough.
As Gordan said, yes, the bandwidth does increase n-fold, but only for
writes; and if you have gigabit ethernet and a decent switch this
should not be too much of a problem. The data still has to go to all
the replicated servers, so it is just the client's interconnect that
has higher utilisation. Unless your workload is very heavy on writes,
this shouldn't be a major problem.
Yes, but if you consider that in a typical setup you have an order of
magnitude more client nodes than server nodes, that starts to add up
pretty quickly.
You can also use write-behind to aggregate writes, which can help
avoid unnecessary overheads caused by making many small writes to the
AFR volumes.
Hmm... Now if writes could happen over multicast, that would be pretty
cool, as the writes wouldn't scale inversely. But I'm guessing this
isn't anywhere on the feature list (yet)...
Gordan
