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#41
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In article ,
John-Paul Stewart wrote: Yes. If you look at the CPUs on RAID cards, they're a lot less powerfull than the host CPU (even on the most expensive $1000+ cards). However, that assumes that there are CPU cycles available on the host (i.e., it is *not* CPU bound, as the previous poster mentioned). If your file server is CPU bound you're doing something seriously wrong. -- I've seen things you people can't imagine. Chimneysweeps on fire over the roofs of London. I've watched kite-strings glitter in the sun at Hyde Park Gate. All these things will be lost in time, like chalk-paintings in the rain. `-_-' Time for your nap. | Peter da Silva | Har du kramat din varg, idag? 'U` |
#42
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Peter da Silva wrote:
In article , John-Paul Stewart wrote: Yes. If you look at the CPUs on RAID cards, they're a lot less powerfull than the host CPU (even on the most expensive $1000+ cards). However, that assumes that there are CPU cycles available on the host (i.e., it is *not* CPU bound, as the previous poster mentioned). If your file server is CPU bound you're doing something seriously wrong. Who said this is limited to discussions of file servers? Database servers (or other specialized application servers) may well be CPU bound and directly connected to a large RAID. |
#43
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"Jon Forrest" wrote in message
John-Paul Stewart wrote: Yes. If you look at the CPUs on RAID cards, they're a lot less powerfull than the host CPU (even on the most expensive $1000+ cards). That's because, other than performing the XOR operations for writes, they don't have to do very much. I haven't seen any benchmarks comparing software RAID to hardware RAID where the host CPU was heavily used. They always seem to be done on otherwise unloaded systems. But then, everything I've read agrees with the previous poster's assesment that hardware RAID will win when the host CPU is otherwise occupied. Right. Even when a server is busy, satisfying read requests and non-RAID- 5 requests shouldn't add much to the load. Most of the work is done by the intelligence built-in to the ATA or SCSI electronics on the disk. The latency imposed by the movement of the arms and platters dominates the latency caused by a busy CPU. For a while I was a big fan of those cheap IDE pseudo-RAID 0 and 1 controllers but I now realize that they really don't provide much benefit compared to just adding more IDE channels since those controllers do so little. That's one reason why you can convert one of those Promise IDE boards into a RAID controller by simply adding a resistor. That was only possible with the original Ultra 66 and 100 boards. Next they used different PCI IDs for Ultra and Fasttrak. Jon |
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