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From Michael Segel <michael_se...@hotmail.com>
Subject Use of SSDs wuz RE: zookeeper & HBase
Date Fri, 09 Jul 2010 14:16:42 GMT

I've 'talked' with a friend in Germany who's been doing a lot of research on SSDs and Informix
(Yes they are still around within IBM...)

Lessons learned: The more expensive solutions (PCI-E) SSD cards don't perform much better
than a controller and SATA SSDs. Although the price is much greater.
Raid 10 still makes sense. 

With respect to HBase/ZK ...

You could put out a couple of boxes with SSDs for ZK nodes. I don't know your budget or types
of boxes...

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)

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: aramakrishnan@languageweaver.com
> To: user@hbase.apache.org
> 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:jgray@facebook.com] 
> Sent: Thursday, July 08, 2010 4:25 PM
> To: user@hbase.apache.org
> 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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