On Wednesday 18 July 2012 00:32:16 Lars Marowsky-Bree wrote: > On 2012-07-17T23:44:13, Arnold Krille <[email protected]> wrote: > > Additionally: If its two direct links dedicated to your storage network, > > there is no reason going active/backup and discarding half of the > > available bandwidth. > Since the system must be designed for one link to have adequate > bandwidth to provide the service (otherwise it could not actually cope > with one link failing), this shouldn't be a significant problem ;-)
That would mean that your system runs the same whether one or two links are present. But fault-tolerant doesn't necessarily mean that performance is the same in the clean and in the faulty state. And selling "two with double throughput but it also works when in fault-state" sells better than "two but you won't see it except for a slightly better fault-tolerance". And then count in the failure-probability of a direct link. Compared to the inter-linked failure-probability of two-port network-cards where still both links are down when the card breaks. Two-port cards only protect against single-cable-failure (with a direct link in the same rack?) or failure of the (physical) network-drivers. When the chip or the cards powersupply fails, both links are down, doesn't matter if active-backup, balance-rr, lacp, or broadcast... And when the scenario is the prototype of HA: one service provided in HA with an active-backup-setup of two machines that do nothing else? then I want the interlink to be as reliable _and_ as fast as possible so I don't loose the last bit of information because the disk-mirroring hasn't pushed out the data fast enough because of using only one 1GB link where two where available. Have fun, Arnold
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