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Re: Hard Drive data rates



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


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