On Friday 28 September 2007, John Wendel wrote: > Lamar Owen wrote: > > On Friday 28 September 2007, John Wendel wrote: > >> Lamar Owen wrote: > >>> Due to the 8B/10B coding used in SATA, you can divide the bitrate by > >>> ten and not eight to get the byterate. Thus, 3Gb/s is 300MB/s at the > >>> wire. > >> > >> Your talking about the wire speed. The REAL speed is determined by the > >> disk drive. You're lucky to get 75MB/s with a desktop drive. > > > > I did say "at the wire" above. > > Indeed you did, and I wasn't questioning your analysis. Sorry! Just > thought I had something interesting to add. Astronomers rule! :) To further analyze, here's bonnie++ results for an external SATA 750GB drive, Seagate model ST3750640AS, on a Silicon Image (SiI) 3132 ExpressCard eSATA II interface, whose hdparm -t results are 64.59MB/s (PC being a Dell Inspiron 640m Core 2 Duo @ 2GHz with 2GB RAM): Sequential Writes, Per Chr: 40MB/s Block Writes: 49MB/s Rewrite: 23MB/s Sequential Reads, Per Chr: 47MB/s Block Reads: 53MB/s Seeks per second: 144.9 In contrast, on a midrange server here running CentOS 4 (3 300GB 15K RPM SAS drives, hardware RAID5), hdparm -t being 108MB/s: Sequential Writes: 36MB/s Block Writes: 115MB/s Rewrites: 23MB/s Sequential Reads: 30MB/s Block Reads: 104MB/s Random Seeks: 1005/s My laptop's internal SATA drive (Hitachi HTS721010G9SA00 on the internal Intel ICH7), hdparm -t being 48MB/s: Seq Writes: 30MB/s Block Writes: 30MB/s Rewrites: 17MB/s Seq Reads: 42MB/s Block Reads: 44MB/s Random Seek: 118.4/s In real contrast, a Seagate FreeAgent Go 160GB USB 2.0 drive (the drive itself is SATA inside the case); hdparm -t being 27.8MB/s: Seq Writes: 24MB/s Block Writes: 25MB/s Rewrites: 11MB/s Seq Reads: 24MB/s Block Reads: 26MB/s Random Seek: 130/s For another comparison, on an SGI Altix 3000 20 CPU box with FC-attached drives, I get: Seq Writes: 17MB/s Block Writes: 139MB/s Rewrite: 50MB/s Seq Reads: 17MB/s Block Reads: 131MB/s Random Seeks per second: 516 Bonnie++ is available in the standard Fedora 7 repositories; yum install bonnie++ should work. It is recommended to uninstall it when done benchmarking; for a desktop or laptop this shouldn't be an issue; the issue is with servers, where, if someone were to break in, bonnie++ makes a handy denial of service mechanism. -- Lamar Owen Chief Information Officer Pisgah Astronomical Research Institute 1 PARI Drive Rosman, NC 28772 (828)862-5554 www.pari.edu
