[Gluster-users] Exorbitant cost to achieve redundancy??

[Arnold Krille]

Hi,

On Monday 13 February 2012 16:15:16 Jeff Wiegley wrote:
> In other words... GlusterFS TRIPLES all my storage costs to provide
> 2 brick fault tolerance?
> How do I get redundancy in GlusterFS while getting reasonable
> storage costs where I am not wasting 50% of my investment or
> more in providing copies to obtain redundancy?

Show me any kind of redundancy without multiplying the efforts!

Take a simple raid1 with two disks: How do you achieve fault-tolerance against 
one failing drive without storing the data on a second disk?
When you need tolerance against two failing disks (at the same time), you have 
to have at least three disks containing the data.

For bigger setups there are raid-levels that work with more then two disks and 
are tolerant against one or two failed drives, but then you "loose" one or two 
disks in your array for checksums. And these have a lot of disadvantages too.

As cheap as disk-space got the last years (save the last 4 months since the 
flood), most admins just use raid1 and be done with it. (Yes, I am an advocate 
of baarf, though not an "official member":)

Now the problem with raid inside one machine is that you still have the 
single-point-of-failure of motherboard, cpu, memory, psu(*), controller and 
network(to a point). With systems like glusterfs, moosefs, drbd and others you 
have your raid span multiple machines removing these spofs while preserving 
the advantage of local disk-reads. When you use the fs that way...

And on a side-note: I don't know what you get per hour but taking low it-wages 
in germany it takes probably less then one man-week of data-recovery to 
amortize the "investment" of doubling disks and machine for redundancy.
And when the data is lost due to missing redundancy, its not only one persons 
work that is lost... The additional hardware pays off faster then your 
boss/client can think about the expenses.

Have fun,

Arnold

(*) Yes, you can have multiple psu in one machine. And thats nice too when you 
switch your machine from one ups to another. But power is still distributed by 
one power-distribution-board. Which is why I count the psu still as a spof.
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