Hello Paulo,
Many thanks for the advice. My application is a geophysical
datalogger that produces a lot of data continuously. Because of this,
in combination with the need for data integrity if there is a power
failure, I expected 'sync' to be the best and most honest mount
choice. My understanding was that 'async' mounts reported optimistic
write speeds for burst data because the dirty data cache absorbed the
slow write speed of the phyical media, but I need sustained write
speeds over many days.
Your point about the efficiency of writing blocks at a time with
'async' mounted media is very interesting and I am looking into that.
However, TS have reported much higher write speeds in their tests
even with the SD card mounted as 'sync'. My real concern though is
that I have done something wrong that prevents me from achieving the
speeds TS have reported to me.
I have tried two brands of SD card, a generic 512Mb 60x card and a
256Mb Kingston card. The generic card is faster than the Kingston
card but not startling so. I have tried using many small or one big
partition, and block sizes of 1kb to 4kb with little difference. All
have ext2 format. I have a 32Mb yaffs root fs. The SD card driver is
mounted with DMA enabled (insmod sdcard.o dmaenable=1).
I would like to know if anyone else has done any sort of benchmark
with the SD card on the TS7260 with sustained writes or 'sync' mounted
media.
Kind regards,
Hamish
> Forcing the kernel to use "sync" mode is very bad for your performance,
> because the kernel won't be able to coalesce any writes, even writes
for
> the same sectors.
>
> It should be much better to use async and to tune your kernel so that
> the dirty data size doesn't grow so much that it becomes a problem.
>
> I hope this helps,
>
> --
> Paulo Marques
> Software Development Department - Grupo PIE, S.A.
> Phone: +351 252 290600, Fax: +351 252 290601
> Web: www.grupopie.com
>
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