At 03:11 AM 3/10/2009, Christian Meisinger wrote:
hi there.
i've 6 load-balanced webservers running with apache 2.0.
right now we use unison to upload file changes from the developers to server 1
and then 'sync' those changes to 2, 3 andsoon.
additionally if a file is created on one of the servers (like a
temporary download created with php)
we 'sync' that file with scp. for safety there are unisons running
every 10mins on some servers
to ensure all files are available on every server.
right now it's not a problem with only 6 servers but i'm pretty sure
it will become a big problem
with more servers...
so i started some tests GlusterFS 2.0.0rc2.
right now i think two setups may suit us:
layout 1:
node1-replicate-node2 \
node3-replicate-node4 - --> distribute ( like raid0 over 3 x raid1 )
node5-replicate-node6 /
or
layout 2:
node1-replicate-node2-replicate-node3 \
node4-replicate-node5-replicate-node6 - --> distribute ( like
raid0 over 2 x raid5 :) )
i think layout 1 should be ok, because until now i've never seen 2
servers crash at the same time.
I'd definitely recommend layout 1 over layout 2. the more nodes in
an AFR brick the more performance issues you may have.
my problem is: what happens if we get additional servers?
if you add them in pairs, you're in good shape, otherwise, you need
to do a 3-node afr brick until you have an even number of servers
then do something different.
i've tested layout 1 with 4 nodes, shutdown GLFS, added
node5-replicate-node6 to the distrubite translator and started
again. files were ok but i got alot of GLFS errors in the log files.
can i safely ignore them?
it depends on which errors they are.. you'd have to use your judgement.
whenever I know a node has failed in an AFR pair, I typicall turn on
"favorite-child" in the other one, remount, then bring up the down
server. then run ls -lR on the server that didn't crash.
once done, remount without favorite child. but this way you don't
get the i/o errors (although I think those are fixed in Rc3 or 4) you
might be seeing.
i know the manual says: use distribute for fresh installations else unify.
still i'm curious if it would work with distribute.
btw. for GlusterFS version 2.0 is AFR = replicate?
yes
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