On Thursday 26 October 2006 21:29, Allen S. Rout wrote: > >> On Wed, 25 Oct 2006 23:34:31 -0500, Roger Deschner <[EMAIL PROTECTED]> > >> said: > > > > You probably want to avoid RAID5 for disk storage pools, whether > > sequential or random. That can really slow client backups, because > > RAID5 is quite slow for writing. RAID5 is really only good for > > read-mostly applications, so at least you'll migrate quickly. You > > probably want RAID10 instead, a striped set of mirrored pairs. (Make > > sure your RAID10 implementation is NOT a mirrored pair of striped > > sets, which is quite unsafe!) RAID10 is a less efficient use of raw > > disk space, but both faster and safer than RAID5. I do not agree. New SAN boxes with write cache (with battery's) are smart. Very smart. New boxes are even better and need less ram to have the same performance. I did some tests on raw devices and I saw NO (repeat NO) performance difference between raid 5 and raid 10.
Sorry for the layout, but this is a copy/paste from an open office document. These are tests done on DS6000 with 75 GB, 1500 RPM disks, 8 disks in a raid and show the difference between raid 10 and raid 5: raid10 -> raid 5 raid type Q Bytes Ops Rate (MB/s) IOPS Latency %CPU 10 random 10 101,55% 101,55% 101,55% 101,55% 100,00% 101,64% 10 seq 10 103,90% 103,90% 103,91% 103,90% 100,00% 103,74% 10 random 5 99,26% 99,26% 99,24% 99,25% 100,00% 99,37% 10 seq 5 99,23% 99,23% 99,19% 99,19% 100,00% 98,83% 10 random 1 101,46% 101,46% 101,46% 101,46% 100,00% 101,39% 10 seq 1 95,51% 95,51% 95,51% 95,51% 100,00% 96,48% average 100,15% 100,15% 100,14% 100,14% 100,00% 100,24% Just forget averything you think to know about raid 5 vs raid 10 IF you have a good SAN box with write cache. I don't know how it works, but the SAN controllers are smart and are acting different on randon I/O vs sequential I/O. Stef
