>> since storage is very cheep, i think this is a good tradeoff. > > I'm thinking of an scale where storage isn't that cheap ...
what scale is that? >> what problem are you trying to solve? if you are trying to go for >> reliability, i would think it would be easier to use raid+backups >> for data stability. > > Easier, yes, but more expensive (at least the iron). not sure what you mean by this. suppose i have 10TB to keep in a redundant fashion. with a two machine solution, i need 20TB of disk since the only sensible way to keep a redundant copy on a second machine is a full mirror. with a 1 machine solution, i don't need any more disks to have a full mirror and i have the option of raid5 which will reduce the number of disks i need to 10TB + 1 disk. since your model is that the storage is a significant expense, a single raid5 machine would make more sense. even if you are thinking of an enormous cloud with hundreds of machines, you could halve the number of machines required by raiding each node. if cost is an issue, reducing the number of machines is a benefit. given constant data, fewer machines reduces the obvious -- power, chassis, etc. but another important reduction is network ports. once you outgrow a single 24-port switch, network costs seem to grow in a super-linear fashion. - erik
