[Gluster-users] Gluster FS replication
israelshirk at gmail.com
Sun Oct 21 21:18:58 UTC 2012
Haris, try the NFS mount. Gluster typically triggers healing through the
client, so if you skip the client, nothing heals.
The native Gluster client tends to be really @#$@#$@# stupid. It'll send
reads to Singapore while you're in Virginia (and there are bricks 0.2ms
away), then when healing is needed it will take a bunch of time to do that,
all the while it's blocking your application or web server, which under
heavy loads will cause your entire application to buckle.
The NFS client is dumb, which in my mind is a lot better - it'll just do
what you tell it to do and allow you to compensate for connectivity issues
yourself using something like Linux-HA.
You have to keep in mind when using gluster that 99% of the people using it
are running their tests on a single server (see the recent notes about how
testing patches are only performed on a single server), and most
applications don't distribute or mirror to bricks more than a few hundred
yards away. Their idea of geo-replication is that you send your writes to
the other side of the world (which may or may not be up at the moment),
then twiddle your thumbs for a while and hope it gets back to you. So,
that said, it's possible to get it to work, and it's almost better than
lsyncd, but it'll still make you cry periodically.
Ok, back to happy time :)
> I am using Gluster in replication mode.
> Have 3 bricks on 3 different physical servers connected with WAN. This
> makes writing but also reading files from Gluster mounted volume very slow.
> To remedy this I have made my web application read Gluster files from
> the brick directly (I make a readonly bind mount of the brick), but
> write to the Gluster FS mounted volume so that the files will instantly
> replicate on all 3 servers. At least, "instant replication" is what I
> envision GLuster will do for me :)
> My problem is that files sometimes do not replicate to all 3 servers
> instantly. There are certainly short network outages which may prevent
> instant replication and I have situations like this:
> ssh web1-prod ls -l
> -rw-r--r-- 1 apache apache 75901 Oct 19 18:00
> ssh web2-prod ls -l
> -rw-r--r-- 1 apache apache 0 Oct 19 18:00
> ssh web3-prod ls -l
> -rw-r--r--. 1 apache apache 75901 Oct 19 18:00
> Where the file on web2 server brick has a size of 0. So serving this
> file from web2 makes my application make errors..
> I have had a brain-split situation couple of times and resolved
> manually. The above kind of situation is not a brain-split and resolves
> and (re-)replicates completly with a simple "ls -l" on the file in
> question from any of the servers.
> My question is:
> I suppose that the problem here is incomplete replication for the file
> in question due to temporary network problems.
> How to insure the complete replication immediatly after the network has
> been restored?
> kind regards
> Haris Zukanovic
> Haris Zukanovic
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