On 2009-07-30, Jan Stary <h...@stare.cz> wrote:
> is 128M, that's why I use xserv45.tgz and not base45.tgz;
> and it should have been tar xzpf I guess - does it make
> a difference? And it shloud be done in single user - but
> the machine is almost idle, really.)

xserv has a small number of large files, whereas base has a mixture,
but it has a lot of small files in it. xzpf won't matter for this test,
but if my theory is right, you will need to write lots of small files
to see a difference.

> For some reason (no reason), I have always thought that nothing can
> be faster than async. What is the rationale for mounting the target
> filesystems async mounts during an install, anyway?

It's a lot faster than mounting them sync. (ramdisks don't have softdep,
and also softdep on OpenBSD doesn't free up space from pending deletes
quickly enough to be a good choice for untarring new OS file sets).

>> I have a feeling softdep may be faster in this case, but it has
>                                          ^^^^^^^^^^^^
>> drawbacks too.
>
> Meaning, a slow IO?
> What's specific about async vs. softdep in this case?

Making many small updates to a single area of disk (like a
directory entry) means a lot of read/write/erase cycles. You can't
just update a few bytes in the middle with flash; the controller
must read a whole flash block (not related to filesystem block
sizes; much larger), make the change, write out the whole block
to a new flash block, and erase the old one.

Softdep and async do totally different things. Softdep collects
metadata updates over a period of time and writes them out together.
AIUI this means you skip a huge number of directory writes in this
use case.

>> The speed rating by itself isn't very useful. The random-access write
>> speed has the biggest effect when used on a computer and since it is
>> hardly relevant to use with a camera, doesn't usually get mentioned.
>
> This confuses me: isn't the write speed very relevant when
> making shots in quick succession, for example?

The key word is *random*, cameras don't do random-access writes,
they buffer to RAM then write sequentially, mostly to blank areas
of the card rather than making small changes to existing stored
data.

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