[sclug] Mirror disks across machines like distributed RAID?

[John Stumbles]

Dickon Hood wrote:
> On Tue, Jan 05, 2010 at 18:42:35 +0000, Keith Edmunds wrote:

> : You seem to be very against DRBD but without stating any real reason.
> 
> I don't mean to be: as I said, I have no experience of it.  I'm just not a
> fan of HA disc; IME it's better to engineer your application so you don't
> need it.
> 
> : In the case, for example, of an HA web server, putting the websites on a
> : DRBD device seems straightforward and reliable. How would you propose
> : doing that in the application layer (and saving the aforesaid bundle)?
> 
> HA webservers can usually be managed happily with the usual tricks:
> clusters of machines, load balancers (if you insist), HSRP-alike failover,
> virtual IP addresses and whatnot.  Or you can simply do what the BBC has
> done for many years, and have a five-minute TTL on the DNS and ifconfig an
> alias on another machine should one of the farm go down.  This sort of
> thing isn't rocket science.

Even with a cluster of webservers they have to have access to the same 
data so surely you've still got to have some sort of HA disc system? I 
know most of the data can be sourced from a master machine and 
replicated across local discs on the slave webservers but there's still 
got to be some flow of data back from the slaves from web forms, cookies 
and what-have-you.

And when you start talking about general purpose filestores with 
people's home directories on them there's surely no way you can engineer 
each and every application the users might run to get round failure of 
one disc?


-- 
John Stumbles                                       http://yaph.org.uk
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