Hard Drive data rates

[John Wendel]

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 at k5di /]# hdparm -t /dev/sda
> 
> /dev/sda:
> Timing buffered disk reads:  164 MB in  3.03 seconds =  54.21 MB/sec
> [root at k5di /]# hdparm -t /dev/sdf
> 
> /dev/sdf:
> Timing buffered disk reads:  190 MB in  3.02 seconds =  62.96 MB/sec
> [root at k5di /]# hdparm -T /dev/sdf
> 
> /dev/sdf:
> Timing cached reads:   1004 MB in  2.00 seconds = 501.56 MB/sec
> [root at k5di /]# hdparm -T /dev/sda
> 
> /dev/sda:
> Timing cached reads:   992 MB in  2.00 seconds = 496.23 MB/sec
> [root at 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