Hi All,

am calculating throughput for my SD card using "dd" in FC7 2.6.21 kernel.

After mounting the sd card, i run,
:
: time dd if=/dev/zero of=/mnt/sdcard/Myfile.txt bs=512
: count=20480;umount /mnt/sdcard;
: 20480+0 records in
: 20480+0 records out
: 10485760 bytes (10 MB) copied, 0.0658825 s, 159 MB/s
:
: real 0m0.097s
: user 0m0.013s
: sys 0m0.055s

But the throughput shown(159 MB/s) exceeds the throughput of SD specification.
Is it a normal behaviour? What is happening while dd?? Has the data been actually written in the SD card??
Can u pls comment on this??

Thanks,
amio

All the data may not be written into the SD card until a sync is issued, un-mounting the device etc. Could you please try "sync" command and let us know the result.

Regards,
Suresh Maniyath

Hi Suresh,
Thanks for ur reply.
Here is the output with sync.
I tried with sync and umount. It also produces higher number of throughputs..

time dd if=/dev/zero of=/mnt/sdcard/Myfile.txt bs=512 count=204800;sync;
204800+0 records in
204800+0 records out
104857600 bytes (105 MB) copied, 0.720001 s, 146 MB/s

real 0m0.724s
user 0m0.115s
sys 0m0.554s

Am not sure why such higher numbers are got for SD card??
Pls help.

Thanks,
amio

I think you are probably seeing a cache issue. Try(as root) using hpdarm -tT /dev/sda (or whatever your sd device is ). The -tT should account for the cache.

Amio,
I don't have a disk to try it. But just for a experiment, can you try the two command's in a shell script and time the script. I have a small doubt in the numbers. This is to see a comparative numbers with your previous post.

As mentioned by lazlow you can try "hdparm" utility also.

Suresh Maniyath

Thanks Lazlow and suresh for ur replies..

I tried the following in FC7 for SD cards

hdparm -tT /dev/BlockDev0

/dev/BlockDev0:
Timing cached reads: 1118 MB in 2.00 seconds = 558.61 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate
ioctl for device
Timing buffered disk reads: 14 MB in 3.13 seconds = 4.47 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate
ioctl for device

Am not sure whether i got the right speed because of the errors "Inappropriate ioctl for device"..

Awainting possible solutions..
Thanks a olot..
Amio

After mounting the sd card, i run,
:
: time dd if=/dev/zero of=/mnt/sdcard/Myfile.txt bs=512
: count=20480;umount /mnt/sdcard;
: 20480+0 records in
: 20480+0 records out
: 10485760 bytes (10 MB) copied, 0.0658825 s, 159 MB/s
:
: real 0m0.097s
: user 0m0.013s
: sys 0m0.055s

But the throughput shown(159 MB/s) exceeds the throughput of SD specification.
Is it a normal behaviour? What is happening while dd?? Has the data been actually written in the SD card??
Can u pls comment on this?
==========

AMIO.PRABA:

There is nothing wrong with your data. Don't worry.
The 159 MB/s is not the size of either your device or the reading. dd does not make pretentions. In your posted data it is very clear that
: 20480+0 records in
: 20480+0 records out
: 10485760 bytes (10 MB) copied
Thats exactly what it is.
The 159 MB/s is the speed in Mega-Bytes-Per-Second that the records were gathered in and accounted out.
So it is only the speed of recording, not the size of device volume.

Go in peace.

Hope this helps.

amio

You do not want to go that deep into the system (/dev/BlockDev0. At the command line simply type mount. This will give you where the system thinks everything is mounted. That is the point you want to run the hdparm test to.

In this case (above) you can tell that /dev/sdb1 is the one I would want to run the test on(linked to /media/FEDORA). /media/something is the standard mount point on Fedora for removable media. Depending on your system I would expect your test to be in the /dev/sdX1 format(X=a,b,c,d,...)

Hi Mustaq,
Thanks for ur explanation.. :-)

Hi Lazlow,
Mount on my system showed /dev/Blockdev0p1 on /mnt/sdcard type ext2 (rw)

I tried "hdparm -tT /dev/BlockDev0p1". But i still get "Inappropriate ioctl for device"..
Are these errors need to be taken into account? Or fine to ignore these??

Thanks,
amio

That is very strange (/dev/BlockDev0p1). Since FC4 on all my different machines(50+ machines over the years) they have always mounted in the /dev/sdX1 format. Are you manually mounting it by any chance?

Hi Lazlow,

I mount my sdcard using my own SD driver and fix the device as BlockDev.
Is it a case that hdparm can only be used on /dev/sdaX..??? :-( .

Still, am not sure about the messages, "HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device" on using hdparm..

Thanks,
Amio

I THINK there are a few layers that are normally between the block device and the normal device. Skipping those layers MAY be the reason for the error you are seeing.