Re: Ye Olde optimization/mirror disk space debate
Please respect my Mail-Followup-To: header.
On Fri, Nov 22, 2002 at 02:07:26PM -0800, Thomas Bushnell, BSG wrote:
> 36GB disks? Why buy 36GB disks when you can buy big ones? See, the
> problem here is that things are in such frequent motion, that what seemed
> like a big disk once is now small. 36GB is a tiny disk.
You did not answer the question of how to scale its capacity according to
your claims about the cost of disk space, for any size disk. The problem
has nothing to do with the increasing size of disks.
But to answer your question...because they're popular and economical.
6 36GB disks @ USD100 ea. = USD600 for 180GB RAID-5 (USD3.33/GB)
3 73GB disks @ USD200 ea. = USD600 for 146GB RAID-5 (USD4.11/GB)
4 73GB disks @ USD200 ea. = USD800 for 219GB RAID-5 (USD3.65/GB)
Your storage requirements are 120GB and you are on a budget. What
configuration do _you_ choose?
You seem to be applying desktop PC economics to server problems, which they
do not accurately model.
IBM makes a 146GB drive for about USD900, by the way. That's USD6.16/GB,
and when it dies, it's gone along with all of the data it held.
> There are plenty of options. My claim is threefold.
>
> 1) The relevant number is how much it costs *us*, provided we do the
> right thing, and make it simple for mirrors to mirror only what
> they wish;
The total cost to us, including the cost of hardware purchase, hardware and
software maintenance (more buildd's? faster buildd's?) and increased
complexity, is more than enough to require demonstrable benefit before
implementing such a system, and the burden of proof is on those who want
this to happen.
> 2) Complaining about "hundreds of megabytes" is complaining about
> trivialities. (I do not dispute that 60GB is worth thinking
> about.)
I never made any statements about "hundreds of megabytes". Personally, I
think that the maintenance and complexity costs far exceed the hardware cost
in the long run, but I had a specific objection with your hardware cost
estimates.
> 3) This discussion requires thinking about actual cost, and not a
> vague idea of how it must not be useful and would be "too
> expensive". We should think what the cost to us actually is, and
> then decide if that's too expensive.
I think that even a conservative estimate of cost is sufficient to show that
this idea must be shown to be useful before resources are allocated to it.
We should decide whether this even makes sense, and then think about the
cost.
--
- mdz
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