Messages in this thread | | | Date | Wed, 9 Dec 1998 07:13:15 -0500 (EST) | From | Christopher Smith <> | Subject | Re: Dumb question: Which is "better" SCSI or IDE disks? |
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On Wed, 9 Dec 1998, Gregory Maxwell wrote: > On Tue, 8 Dec 1998, Christopher Smith wrote: > > On Tue, 8 Dec 1998, Leonard Zhang System Administrator ISD RVIB wrote: > > > RAID-1 is disk mirror. DPT is cache with RAID. RAID will increase the > > > disk performance. > > Ugh.. FYI, RAID does not always increase disk performance, and in > > particular RAID-1 is guarunteed not to increase disk performance by it's > What? Join the real world but. Raid-1 doubles read throughput and the > slowdown of writes is negligable. A correctly behaving RAID-1 system needs to be able to account for the fact that given disk will fail, so interleaving reads is not exactly a good idea.
> > very nature (ok, it's conceivable that read performance could be > > increased somewhat, but write performance would, if anything, be decreased > > somewhat). Again, if the cache is actually playing a role in this > > benchmark, then what you are really saying is that IDE is so fast that > > it's 4x faster than DPT's cache memory. Think about that for a minute. > Come off it, when you do disk benchmarks you use a dataset sufficently > large so that the cache doesn't matter. Linux does caching just fine, > DPT's cache is somewhat redundant. His system wasn't Linux, it was SCO. If you looked at his data set size, it was 9 MB and his cache was 32 MB. So yes, his benchmark was completely inappropriate which is what everyone is trying to point out here.
> Almost all other raid levels perform worse (like raid 5 where the fastest > write takes 2 reads 1 block XOR and 1 write). You are talking about latency, not thoroughput. Read up on RAID, RAID-0 is not the only version of RAID with performance advantages.
> The fastest raid array is a combo of raid-0(striping) and raid-1. Why would this be faster than just RAID-0?
--Chris
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