Mailinglist Archive: opensuse (880 mails)

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Re: [opensuse] Slow file copying on openSUSE 12.3


Roger Oberholtzer <roger@xxxxxx> wrote:
On Thursday, August 15, 2013 08:13:02 AM Per Jessen wrote:

Wouldn't/couldn't openSUSE be controlling that?

I don't think so, no - I don't know of anywhere in openSUSE where
you're
able to specify it.

Via hdparam perhaps? Another person in this thread reported that their
disk
also has write cache enabled. And that was on a laptop where power loss
is
more common than a system on a UPS. So maybe more poeple have this than

expect.

I just checked a few more 12.3 systems, and I see things like:

sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled,
<snip>

Perhaps I am looking at this in the wrong way?

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

Greg
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