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2TB SATA III HDD via USB 3.0/2.0 external enclosure 500GB SATA II HDD via USB 2.0 external enclosure Both hooked up to Raspberry Pi, no hubs or other USB devices being used

Both disks are mostly empty. Since USB 2.0 is supposed to be 480Mbit/s, and the drives can probably do 50-100MB/s reading/writing. I would expect at least 10-20MB/s transfer speed, but I'm only getting around 5MB/s. Any ideas?

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Are you doing any sort of concurrent reading/writing to either of the drives while using it? Is it possible either drive is highly fragmented? Are the usb and sata cables in good shape? (Damaged cables lead to lots of signal loss and errors.) Anything in /var/log/syslog or /var/log/dmesg? – Stephan Feb 6 '13 at 3:15
No other reading/writing is being done. Both drives were mostly empty so I don't think they'd be fragmented. Both external enclosures are brand new, so there's no cable problems. demsg looked fine, as far as I can tell both enclosures are connected via USB 2.0 high speed. I just checked syslog and noticed 'NTFS-fs error (device sda1): ntfs_readdir(): Directory index record with vcn 0x0 is corrupt. Corrupt inode 0xd0f2. Run chkdsk.' (FYI, I finished copying the 500GB disk and am now copying a mostly full 500GB disk). I'll try chkdsk and see if it helps. – Seán Hayes Feb 6 '13 at 23:50
The NTFS-fs error sounds like a clue to me; lemme know if chkdsk helps! – Stephan Feb 7 '13 at 0:52
I fixed the chkdsk error but it's still only around 5MB/s. – Seán Hayes Feb 7 '13 at 1:20
I'd be suspect of one of the drives being defective at this point; if you have a different hard drive to try, that would rule this out. – Stephan Feb 7 '13 at 1:29

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