Re: Flashbench
On 04/18/2012 07:58 AM, Peter Easthope wrote:
On Sat, April 14, 2012 11:38 pm, Bob wrote:
8< snip 8<
... I haven't yet figured out
what open AUs are and what to do with them, I got slightly disheartened
when on my OCZ SSD drive it didn't seem to make any difference to speed
where I started the partition, I need to try again with a CF or SD card,
maybe it was a buffering thing.
How about AU = allocation unit? No clear idea of
how this relates to the HDD sector or the Flash page.
From perusing the README it seems to be referring to the number of
allocation units that can be open at any given moment without impacting
performance too badly. [0] I don't know how any of that helps tho as I
don't know what to do with that number, is there some-way of instructing
the kernal to limit the number of open AUs?
My 32GB SanDisk Ultra SDHC card, starts to slow down with 6 open AUs
./flashbench -O --erasesize=$[8 * 1024 * 1024] --blocksize=$[256 * 1024] ${trg} --open-au-nr=1 --random
8MiB 4.32M/s
4MiB 7.58M/s
2MiB 12.6M/s
1MiB 18.6M/s
512KiB 17.4M/s
256KiB 11.8M/s
./flashbench -O --erasesize=$[8 * 1024 * 1024] --blocksize=$[256 * 1024] ${trg} --open-au-nr=3 --random
8MiB 9.27M/s
4MiB 18.9M/s
2MiB 18.9M/s
1MiB 18.7M/s
512KiB 17.5M/s
256KiB 11.7M/s
./flashbench -O --erasesize=$[8 * 1024 * 1024] --blocksize=$[256 * 1024] ${trg} --open-au-nr=5 --random
8MiB 9.85M/s
4MiB 12.2M/s
2MiB 11.5M/s
1MiB 18.7M/s
512KiB 17.7M/s
256KiB 11.8M/s
./flashbench -O --erasesize=$[8 * 1024 * 1024] --blocksize=$[256 * 1024] ${trg} --open-au-nr=6 --random
8MiB 11.6M/s
4MiB 12.6M/s
2MiB 14M/s
1MiB 12.8M/s
512KiB 7.64M/s
256KiB 6.38M/s
./flashbench -O --erasesize=$[8 * 1024 * 1024] --blocksize=$[256 * 1024] ${trg} --open-au-nr=7 --random
8MiB 10.3M/s
4MiB 12.6M/s
2MiB 8.16M/s
1MiB 6.46M/s
512KiB 5.54M/s
256KiB 2.5M/s
./flashbench -O --erasesize=$[8 * 1024 * 1024] --blocksize=$[256 * 1024] ${trg} --open-au-nr=8 --random
8MiB 8.93M/s
4MiB 12.4M/s
2MiB 7.76M/s
1MiB 6.12M/s
512KiB 3.26M/s
256KiB 2.02M/s
When / if I get time I'll condense this down a bit and send it into the
flashbench mailing list.
This also helped.
http://wiki.laptop.org/go/How_to_Damage_a_FLASH_Storage_Device
Will aim to work on it again in late May or in June.
Thanks for the notes, ... Peter E.
Thanks for the link, we'll get to the bottom of this in the end,
hopefully someone who knows what's going on will put flashbench in the
repositories with a good man page
[0] Some not very relevant musings. Since a hard-drive cannot physically
do more than one I/O at once we simulate that ability by giving them
clever controllers, buffers and command queues then we more or less
treat them as a black box of storage. I don't know if an individual
flash memory chip can perform multiple simultaneous I/O but even if it
can't, if the SSD or memory card is based on more than one chip then the
question becomes can the controller support simultaneous I/O.
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