Hi, On Wed, Jun 04, 2008 at 11:35:33PM -0700, David Lang wrote: > On Wed, 4 Jun 2008, Dejan Muhamedagic wrote: > >> Hi, >> >> On Wed, Jun 04, 2008 at 01:16:31AM +0200, Lars Marowsky-Bree wrote: >>> On 2008-06-03T16:35:22, "Hildebrand, Nils, 232" >>> <[EMAIL PROTECTED]> wrote: >>> >>>>> - [Quality not important for hardware?] >>>> I think the truth is somewhere in between. If you have a cluster it is >>>> not that important if a node goes down (depending on how available your >>>> services have to be). >>> >>> Right, but telling customers to save on hardware because they are >>> getting clustering is, uhm, not something I'd advocate ;-) >> >> Indeed. Clusters are not a replacement for good hardware. A >> perfect cluster is one which is never exercised (unless when >> testing) ;-) > > I will disagree with this. I've seed companies spend insane amounts of > money on hardware that is internally redundant (to the point of having > nultiple motherboards and cpus running in lock-step and periodicly > cross-checking their results) when a cluster on much cheaper hardware would > have been the right thing to do. > > and ignoring this extreme case it can still be better (both in reliability > and in cost) to buy 2 single-drive/single-power boxes and set them up in a > cluster then to buy 1 fully redundant box, and with a good cluster > implementation (like heartbeat) the difference in total reliability between > a cluster build from two fo the cheap boxes and one built with two of the > expensive boxes can be very small. > > I'm asuming for the example above that both the 'cheap' and 'expensive' > boxes are purchased from the same company. > > a perfect cluster is not one that is never excercised, it's one that > provides uninterrupted service to it's clients.
Hard to argue with this. > A cluster can do this in > the face of many upgrades (including hardware forklift upgrades, OS > upgrades, kernel upgrades, reboots, etc) that no single box solution can > match, no matter how much more you spend on the hardware. True. A cluster is of great help with management/maintenance and that's one important aspect which is sometimes overlooked. Please note that I wasn't arguing about having a single computer vs. clustered computers. The latter should obviously be preferable. But I still maintain that cluster software can't always save you from hardware which is, er ... not robust enough. Probably one doesn't always need ultimate technology, as what you mentioned above, but for example having a redundant power supply is for most HA solutions a very good investment. One can of course save, but one should know where to save. There are quite a few ways hardware can fail which could give you (and the cluster) hard time dealing with it. Not to talk about clusters which are run/planned/configured in a less than optimal way. We may argue about this point being irrelevant, but that's unfortunately a fact of life and has to be taken into account. In short, I don't think there's a single answer to how an HA solution is to be implemented, but for most people and in most situations having reliable hardware can go a long way. Thanks, Dejan > > David Lang > _______________________________________________ > Linux-HA mailing list > [email protected] > http://lists.linux-ha.org/mailman/listinfo/linux-ha > See also: http://linux-ha.org/ReportingProblems _______________________________________________ Linux-HA mailing list [email protected] http://lists.linux-ha.org/mailman/listinfo/linux-ha See also: http://linux-ha.org/ReportingProblems
