[lug] 1T + SATA 300 performance

[Zan Lynx]

On Thu, 2008-03-20 at 11:42 -0700, karl horlen wrote:

> 1237 / 60 secs per minute = 21 minutes to complete
> 232GB job at SATA 1.5Gb speed.  Meaning it should be
> even faster if at 3G speed!
> 
> Is this semi accurate?

No.  You are counting only the SATA link speed which is so fast that it
doesn't really matter.  It only matters if you're using an enclosure
that expands one connection to many drives.

Possible bottlenecks are:
      * The source drive for your copy.
      * The PCI bus.  From your description you are using an add-on PCI
        card.  The ordinary PCI bus is limited to about 100 MB/s after
        considering overhead.  When copying data, halve that to 50 MB/s
        because it must read it then write it back.
      * The target drive.  Even the fastest rotating hard drives peak at
        about 90 MB/s and they slow down toward the end of the disk to
        50 MB/s.

Using 50 MB/s as a rate, 233 GB should take 1.3 hrs.  If your old ATA
drive wasn't exceptional, it very likely does less than 50 MB/s, so the
2 hrs is easy to believe.
-- 
Zan Lynx <zlynx at acm.org>
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