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Re: Hard Drive data rates



Karl Larsen wrote:
Dave Stevens wrote:
On Friday 28 September 2007 03:00:11 pm Karl Larsen wrote:
Dave Stevens wrote:
On Friday 28 September 2007 10:50:32 am Karl Larsen wrote:
    I was lead to mis-understand the data rate of my new SATA hard
drive. It indicated that the data rate was 3 GB/sec. But

you have to tell it what drive to check, so #hdparm -iItT /dev/sda for example, if your SATA drive is the first one.

Dave
Yes but I am amazed by the results when hdparm is used right. Here is what I got 5 minutes ago:

[root k5di /]# hdparm -t /dev/sda

/dev/sda:
Timing buffered disk reads:  164 MB in  3.03 seconds =  54.21 MB/sec
[root k5di /]# hdparm -t /dev/sdf

/dev/sdf:
Timing buffered disk reads:  190 MB in  3.02 seconds =  62.96 MB/sec
[root k5di /]# hdparm -T /dev/sdf

/dev/sdf:
Timing cached reads:   1004 MB in  2.00 seconds = 501.56 MB/sec
[root k5di /]# hdparm -T /dev/sda

/dev/sda:
Timing cached reads:   992 MB in  2.00 seconds = 496.23 MB/sec
[root k5di /]#

   So it appears that a SATA is just a tiny bit faster than a new IDE.



"Timing buffered disk reads:" is the interesting number.

"Timing cached reads:" doesn't measure the disk speed, it measures how fast your system can transfer data from the kernel buffers to the user buffers (memory to memory copy).

Regards,

John



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