On Thu, April 14, 2011 20:54, Andrew Sullivan wrote:
> On Thu, Apr 14, 2011 at 12:27:34PM -0600, Scott Marlowe wrote:
>
>>> That's what a UPS and genset are for. Â Who writes critical stuff to
>>> *any*
>>> drive without power backup?
>>
>> Because power supply systems with UPS never fail.
>>
>
> Right, there's obviously a trade-off here. Some of this has to do
> with how much your data is worth vs. how much the speed is worth. There's also
> the issue of whether you can stand to lose a few rows, and whether you can
> stand to lose them for a short time. For instance, collecting user comments
> might be a matter of great value, but if you write them to more than one
> system, you might not care whether one of the systems fails briefly. In that
> case, maybe big redundancy of cheap disks with power backup is good enough to
> meet the price:value ratio. On stock trades worth maybe millions of dollars,
> not so much: you miss your teeny window of opportunity to do a trade and
> suddenly you're out in the street wearing a barrel.
>
> I can think of lots of different points to be along that continuum,
> and surely nobody is suggesting that there is one right answer for everything.
Exactly. To address the issue of something going wrong (it will, given enough
time), we recently started trying out Pg's built-in replication (we were using
Londiste - nothing wrong with it, but life is simpler now that the Pg
overlords have realised what everyone has known for a long time).
When the super-fast SSD-based machine fails, switching to a (slower) standard
hard-drive based machine provides continuity and buys time while we get the
primary machine back online.
For us, life is better, thanks to SSDs.
h
