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From Mark Kerzner <mark.kerz...@shmsoft.com>
Subject Re: Using a hard drive instead of
Date Fri, 12 Oct 2012 04:27:37 GMT
Harsh,

I agree with you about many small files, and I was giving this only in way
of example. However, the hard drive I am talking about can be 1-2 TB in
size, and that's pretty good, you can't easily get that much memory. In
addition, it would be more resistant to power failures than RAM. And yes,
it has the performance of RAM, and can accommodate very many threads.

Mark

On Thu, Oct 11, 2012 at 11:16 PM, Harsh J <harsh@cloudera.com> wrote:

> Hi Mark,
>
> Note that the NameNode does random memory access to serve back any
> information or mutate request you send to it, and that there can be
> several number of concurrent clients. So do you mean a 'very fast hard
> drive' thats faster than the RAM for random access itself? The
> NameNode does persist its block information onto disk for various
> purposes, but to actually make the NameNode use disk storage
> completely (and not specific parts of it disk-cached instead) wouldn't
> make too much sense to me. That'd feel like trying to communicate with
> a process thats swapping, performance-wise.
>
> The too many files issue is bloated up to sound like its a NameNode
> issue but it isn't in reality. HDFS allows you to process lots of
> files really fast, aside of helping store them for long periods, and a
> lot of tiny files only gets you down in such operations with overheads
> of opening and closing files in the way of reading them all at a time.
> With a single or a few large files, all you do is block (data) reads,
> and very few NameNode communications - ending up going much faster.
> This is the same for local filesystems as well, but not many think of
> that.
>
> On Fri, Oct 12, 2012 at 9:29 AM, Mark Kerzner <mark.kerzner@shmsoft.com>
> wrote:
> > Hi,
> >
> > Imagine I have a very fast hard drive that I want to use for the
> NameNode.
> > That is, I want the NameNode to store its blocks information on this hard
> > drive instead of in memory.
> >
> > Why would I do it? Scalability (no federation needed), many files are
> not a
> > problem, and warm fail-over is automatic. What would I need to change in
> the
> > NameNode to tell it to use the hard drive?
> >
> > Thank you,
> > Mark
>
>
>
> --
> Harsh J
>

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