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On Sunday 31 July 2011 15:17:16 Joshua Murphy wrote: |
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> There probably is a fair chunk of difference in maximum speed the disk |
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> can work at on each end (I've even seen around a 20MB/s difference on |
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> several 160GB drives I've dealt with), but outside of some older |
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> drives that've been heavily abused in their lives, I'm not sure I've |
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> seen a sata drive that I've used my usual drive test (MHDD on a |
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> Hiren's bootable USB) on register below around 60MB/s on the slow end, |
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> and USB2's *theoretical* limit is 480Mb/s (60MB/s) ... real-world |
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> implementations rarely reach, let alone top, around 40MB/s, so disk |
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> speed variation across the disk is an unlikely source of the slowdown. |
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Sounds entirely reasonable, and I wasn't really trying to blame the slowness |
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on that variation - just mentioning it in passing. |
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> More likely, it's the fact that parted has to start from the end, and |
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> work its way backwards, reading, writing, and verifying in separate |
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> rotations of the disk with no benefit from the drive's ability to |
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> stream a larger block into cache, since the whole process is backwards |
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> compared to the streaming read most drives are optimized for. |
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Perhaps I'm naive here, but I should have thought an intelligent disk |
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copying algorithm would be able to account for that, at least in part. Maybe |
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that's why it ran the speed tests at the beginning. |
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> Of course, this is all off the cuff conjecture on my part, including my |
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> assumptions about how parted approaches the whole task... mixed with a |
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> bit of anecdotal evidence on my end... but, makes for amusing |
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> conversation and contemplation, if nothing more substantial. |
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Indeed. |
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> I will point out that the newer advanced format WD 500GB blue's I've |
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> worked recently with pulled a consistent 120-110MB/s speed from end to |
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> end... when their older 320s usually peaked at around 85 or so. |
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Well, I haven't run any proper tests, but watching gkrellm during an |
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occasional large transfer I don't remember seeing more than half that lower |
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figure. These are two Samsung Spinpoint F3 1TB disks in md-raid with LVM-2, |
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and I haven't fiddled with any of their settings. |
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-- |
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Rgds |
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Peter Linux Counter 5290, 1994-04-23 |
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