On Mon, 13 Sep 2004 05:20, Adrian 'Dagurashibanipal' von Bidder <[EMAIL PROTECTED]> wrote: > > Machines that can handle such an IO load have faster CPUs. So for any > > but the very biggest machines there is no chance of CPU performance being > > a problem for RAID-5. > > You certainly have more experience than I - I was thinking about machines > where the CPU is already heavily loaded by userspace tasks, where the > additional load from RAID5 might be a poblem. Don't know for certain, > though.
If you have a machine that is capable of 1296MB/s for RAID-5 calculations (as my P3-650 is), and if that machine has disk IO capacity of 200MB/s (not the maximum that you could achieve with such hardware, but better than the vast majority of such machines) then in theory you will use 15% of your CPU time. But considering that a bus-mastering hardware RAID device will take some RAM access time away from the CPU and that the RAM bandwidth is often the CPU performance bottleneck it's quite likely that a large portion of that 15% CPU performance hit will happen no matter how you attach your disks. It would be really useful if someone spent a couple of weeks benchmarking these things and wrote a magazine article about it. -- http://www.coker.com.au/selinux/ My NSA Security Enhanced Linux packages http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark http://www.coker.com.au/postal/ Postal SMTP/POP benchmark http://www.coker.com.au/~russell/ My home page -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
