[Yaffs] Re: It takes long to write to a large file

On 06-09-15 10:58 -0700, goog long wrote:

>    The log below is for the test of writing 40 MB file. My questions are
>    1) Why does it take much longer for YAFFS2 to write the same 40 MB file
>    compared to JFFS2?
>    2) After writing the file, I remove the file and write it again. Why does
>    it take much longer?
>    At the moment, I can only think of one reason. JFFS2 compressed the data
>    before writing to flash, so for
>    1) JFFS2 writes much less data and it takes less time.
>    2) After deleting the file, eraseing the flash is deferred to the
>    subsequent writes. Because YAFFS2 data is uncompressed, it takes more time
>    to erase more data.

That sounds very plausible. I am surprised at the size of the
difference though. How compressible is the data in this file? How much
space does it take up on the JFFS2 filesystem and on the YAFFS2
filesystem? Obvioulsy the more compressible the data, the more the
test will favour JFFS2.

Could you repeat the test with a file which is already compressed
(gzipped, or perhaps a media file)? It would be very interesting to
see how that affects the results.

(Your comparitive testing is very interesting - do please keep it up,
and I presume you will report your full results in due course).

It is becoming clear that measuring the performance of these
filesystems is actually quite a tricky thing to do, and which will
perform best is highly dependent on the usage scenario.

Wookey
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