On 07/09/2010 07:16 AM, Michael Segel wrote:
Patrick H recommends 5 ZK nodes in a production cluster. I don't disagree, but
feel that you could get away with 3 and still have a window for maintenance...
however... if you can measure you down time in terms of $100.00s per hour or
more, the 5 ZKs are still pretty cheap. (Or rather 3ZKs and then run a ZK on
the name node, and a ZK on your secondary.)
(Then you only have to build out 3 boxes, and put a second set of drives on the
name node and secondary)
Michael, that's pretty close, really it's more like "use 5 ZK servers in
a production online serving cluster where you care about reliability".
The beauty of ZK is that it's up to you - if you like to run 1 server
that's fine from ZK perspective, you just won't have a high
reliability/availability system. 3 server cluster will support 1 failure
w/o loss of service, which is probably fine for most users (this is by
far the most common I've seen). But if you want to be safe use 5. 5
allows you to take 1 server out for maintenance and still be able to
withstand a second unexpected failure w/o interruption of service.
Patricik
I haven't tried this out yet... my guess is that you probably won't see a large
enough performance increase to justify the expense...
JMHO
-Mike
PS. I've been watching the prices of SSDs for a different application. I now
see Crucial's SATA III SSDs are actually cheaper than their SATA II drives.
From: [email protected]
To: [email protected]
Date: Thu, 8 Jul 2010 19:38:22 -0500
Subject: RE: zookeeper& HBase
Good to know ZK is IO intense.
Since ZK does not require much disk space and is IO intense. Has anyone played
with using solid state drives for ZK.
We have a 20 node cluster. It would be feasible to have a 3 node ZK all
configured with solid state drives.
Thanks
Arun
-----Original Message-----
From: Jonathan Gray [mailto:[email protected]]
Sent: Thursday, July 08, 2010 4:25 PM
To: [email protected]
Subject: RE: zookeeper& HBase
ZK is sensitive to IO starvation which is why it is recommended to keep it on a
separate node or separate disk. In most cases, giving ZK its own disk is
sufficient and dedicated node(s) are unnecessary.
On smallish clusters like 10 nodes, I would recommend starting with just 1 ZK
node co-located with your NameNode and HMaster, but with a dedicated disk just
for ZK. Since the NN is a SPOF, having one ZK doesn't really lower your fault
tolerance, except that it may be on a non-raided disk. I encourage RAID usage
for NN and ZK. JBOD for DN/RS.
JG
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