Mailinglist Archive: opensuse (880 mails)

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Re: [opensuse] Slow file copying on openSUSE 12.3
  • From: Per Jessen <per@xxxxxxxxxxxx>
  • Date: Thu, 15 Aug 2013 15:27:46 +0200
  • Message-id: <kuil0r$jsb$1@saturn.local.net>
Greg Freemyer wrote:

I think Per is wrong. Write cache enabled on a sata drive is normal.
But it is small and the drive itself can flush it during a power off
event.

Fyi: per Linus, disk cache is internally organized in track size
chunks. A typical track can hold 1mb, so a 8mb cache on the drive
controller can only hold 8 tracks at a time and that is shared by read
and write. Thus at max when power dies the drive needs to seek 8
times and let the disk spin one rotation.

And the seeks will be done in elevator order, so its not 8 worst case
seeks. So that can be done in about 100 millisecs. Thus a capacitor
to hold a tenth of a seconds power is all the drive needs.

I _was_ wondering if the disk would have something like that.

I suspect Per is used to enterprise gear with bigger caches. The
bigger the cache the more dangerous it is.

Terabyte size drives often come with 64Mb cache, but it's probably still
only 8Mb for writing.


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Per Jessen, Zürich (22.9°C)
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