Comment 76 for bug 119730

I have similar problems.

$ sudo hdparm -tT /dev/sda

/dev/sda:
 Timing cached reads: 3510 MB in 2.00 seconds = 1754.82 MB/sec
 Timing buffered disk reads: 264 MB in 3.02 seconds = 87.49 MB/sec

hdparm -i shows it in udma6 mode. BUT, copy large files shows a transfer rate of ~5MB/s. Occasionallly, it ranges from 2MB/s to 10MB/s.

I tried some other copying tests and found interesting results. My WD 750gb SATA drive has both ext3 and NTFS partions on it. Since I wasn't sure what was the limiting factor that is make the transfer so slow, I copied a 500MB file in/out for both NTFS and exts into/out of /dev/shm, as it can be assumed the RAM disk has the ultimate read/write speeds. Here are the rough results:

NTFS to NTFS: full speed (~70-80MB/s)
NTFS to /dev/shm: full speed
/dev/shm to NTFS: full speed
ext3 to ext3: SLOW (~5MB/s)
ext3 to /dev/shm: SLOW
/dev/shm to ext3: FULL SPEED

That was the surprising part. Copying from RAM disk to ext3 gave me full speed! So I conclude that the problem is in the read speed. Write speed is perfectly fine. FYI, my ext3 is already mounted with the noatime option. Any comments?