[Gluster-devel] replicate with 5 nodes - and adding more nodes in the future

[Krishna Srinivas]

On 6/25/07, Shai DB <dbshai at gmail.com> wrote:
> Hello, we are testing glusterfs 1.2 and I have few questions -
>
>
> 1. we are going to store millions of small jpg files that will be read by
> webserver - is glusterfs good solution for this ?

Yes, definitely.

> 2. we are going to run both server+clients on each node together with apache
>
> 3. replicate *:2
>
> the way i think doing replicate is defining on each server 2 volumes and
> using AFR:
>
> server1: a1, a2
> server2: b1, b2
> server3: c1, c2
> server4: d1, d2
> server5: e1, e2
>
> afr1: a1+b2
> afr2: b1+c2
> afr3: c1+d2
> afr4: d1+e2
> afr5: e1+a2
>
> and then unify = afr1+afr2+afr3+afr4+afr5 with replicate option
>
> is this correct way ?
> and what to do on the future when we add more nodes ? when changing the afr
> (adding and changing the couples) making glusterfs
> redistribute the files the new way ?

Yes this is the right way. If you add one more server f, the one solution
is to move contents of a2 to f2 and clean up a2 and have it as following:

afr5: e1 + f2
afr6: f1 + a2

Cant think of an easier solution.

But if we assume that you will always add 2 servers when you want to add,
we can have the setup in following way:
afr1: a1 + b2
afr2: b1 + a2
afr3: c1 + d2
afr4: d1 + c2
afr5: e1 + f2
afr6: f1 + e2

Now when you add a pair of servers to this (g, h):
afr7: f1 + h2
afr8: h1 +f2

Which is very easy. But you will have to add 2 servers everytime.
The advantage is that it is easier to visualize the setup and add
new nodes.

Thinking further, if we assume that you will replicate all the files
twice (option replicate *:2) you can have the following setup:
afr1: a + b
afr2: c + d
afr3: e + f

This is a very easy setup. It is simple to add a fresh pair (afr4: g +h)

You can have whatever setup you want depending on your
convinience and requirement.

>
> 4. what happens when a hard drive goes down and replaces, the cluster also
> redistribute the files ?

When a hard drive is replaced, missing files will be replicated from the
AFR's other child.

Regards
Krishna

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