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From: Todd Lipcon <todd@cloudera.com>
Date: Thu, 25 Oct 2012 06:08:06 -0700
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Subject: Re: HDFS HA IO Fencing
To: user@hadoop.apache.org
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Hi Liu,

Locks are not sufficient, because there is no way to enforce a lock in a
distributed system without unbounded blocking. What you might be referring
to is a lease, but leases are still problematic unless you can put bounds
on the speed with which clocks progress on different machines, _and_ have
strict guarantees on the way each node's scheduler works. With Linux and
Java, the latter is tough.

You may want to look into QuorumJournalManager which doesn't require
setting up IO fencing.

-Todd

On Thu, Oct 25, 2012 at 1:27 AM, lei liu <liulei412@gmail.com> wrote:

> I want to use HDFS HA function, I find the  IO Fencing function is
> complex in hadoop2.0. I think we can use  file lock to implement the  IO
> Fencing function, I think that is simple.
>
> Thanks,
>
> LiuLei
>


-- 
Todd Lipcon
Software Engineer, Cloudera

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Hi Liu,<div><br></div><div>Locks are not sufficient, because there is no wa=
y to enforce a lock in a distributed system without unbounded blocking. Wha=
t you might be referring to is a lease, but leases are still problematic un=
less you can put bounds on the speed with which clocks progress on differen=
t machines, _and_ have strict guarantees on the way each node&#39;s schedul=
er works. With Linux and Java, the latter is tough.</div>

<div><br></div><div>You may want to look into QuorumJournalManager which do=
esn&#39;t require setting up IO fencing.</div><div><br></div><div>-Todd<br>=
<br><div class=3D"gmail_quote">On Thu, Oct 25, 2012 at 1:27 AM, lei liu <sp=
an dir=3D"ltr">&lt;<a href=3D"mailto:liulei412@gmail.com" target=3D"_blank"=
>liulei412@gmail.com</a>&gt;</span> wrote:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">I want to use HDFS HA function, I find the=
=A0 IO Fencing function is=A0 complex in hadoop2.0. I think we can use=A0 f=
ile lock to implement the=A0  IO Fencing function, I think that is simple.<=
br>

<br>Thanks,<br><br>LiuLei<br>
</blockquote></div><br><br clear=3D"all"><div><br></div>-- <br>Todd Lipcon<=
br>Software Engineer, Cloudera<br>
</div>

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