Software and hardware annotations 2010 January

This document contains only my personal opinions and calls of judgement, and where any comment is made as to the quality of anybody's work, the comment is an opinion, in my judgement.

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100117 Sun Big difference in disk transfer rates with different PCs

So I got a new PC some time ago but I kept around the old PC upgrading it a bit. Today I used a fast 1TB eSATA disk drive on both and noticed a difference in speed. So I tried the simplest speed test and the raw difference is quite significant:

soft# cat /sys/block/sda/device/model 
ST31000322CS    
soft# hdparm -tT /dev/sda

/dev/sda:
 Timing cached reads:   2028 MB in  2.00 seconds = 1012.54 MB/sec
 Timing buffered disk reads:  226 MB in  3.02 seconds =  74.84 MB/sec

base# cat /sys/block/sde/device/model 
ST31000322CS    
base# hdparm -tT /dev/sde

/dev/sde:
 Timing cached reads:   14712 MB in  2.00 seconds = 7362.36 MB/sec
 Timing buffered disk reads:  334 MB in  3.02 seconds = 110.67 MB/sec

The buffer cache read bandwidth is massively different, in part because the old PC had a socket 754 Athlon 64, so with only a 64 bit memory channel and at 400Mhz. Quite impressive anyhow, especially for the absolute bandwidth of the new PC.

As to disk transfer rate, the old PC is 32% slower probably because of an older chipset and the host adapter being on a PCI rather than PCIe bus (which has much better bandwidth).