how to test SD read/write speed

**macakinho** · May 10th, 2009

Hi!

Just got a brand new SD card off ebay, but bought it from a seller in Hong-Kong and when I got it, it wasn't the same brand as advertised... in fact, it didn't have any brand at all..

It has a sticker in it saying it is a class 6 device.

How can I test its read/write speed?
Looked all over and found nothing for Linux...

Cheers!

**StuartN** · May 10th, 2009

Originally Posted by macakinho

How can I test its read/write speed?

Find out which device it mounts as and run hdparm -t. For instance, if I plug a USB pendrive in it mounts as /dev/sdb:

Code:

sudo hdparm -t /dev/sdb

/dev/sdb:
Timing buffered disk reads:   58 MB in  3.10 seconds =  18.70 MB/sec

**macakinho** · May 10th, 2009

Originally Posted by StuartN

Find out which device it mounts as and run hdparm -t. For instance, if I plug a USB pendrive in it mounts as /dev/sdb:

Code:

sudo hdparm -t /dev/sdb

/dev/sdb:
Timing buffered disk reads:   58 MB in  3.10 seconds =  18.70 MB/sec

Thank you!
This only gave me the write speed though... Read the ma hdparm and didn't find any option to test the write or erase speed.
Any help here?

**danwood76** · May 10th, 2009

You can use DD to test disk speed, but it can easily lead to damaged data (partitions) if used incorrectly but is probably the most direct way of testing.

So for example my second internal disk is mount /media/HD2 so running this gives me the write speed:

Code:

dd count=1k bs=1M if=/dev/zero of=/media/HD2/test.img
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 7.69365 s, 140 MB/s

that command writes 1GB to the disk, this large number is because the filesystem on the device will speed up the transfer by caching the data if a small transfer is carried out.

--edit--
This is a VERY dangerous command if you miss-type the output file so obviously take care using it and be sure to type correctly!

**macakinho** · May 10th, 2009

Originally Posted by danwood76

Code:

dd count=1k bs=1M if=/dev/zero of=/media/HD2/test.img
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 7.69365 s, 140 MB/s

Thanks! That did it!

I'm really disappointed now...
sticker on SD card: "Class 6"
terminal: "1073741824 bytes (1.1 GB) copied, 212.248 s, 5.1 MB/s"
wikipedia : "Class 4"

**danwood76** · May 10th, 2009

It could be your card reader/writer that is slower as opposed to the card?

**macakinho** · May 10th, 2009

Originally Posted by danwood76

It could be your card reader/writer that is slower as opposed to the card?

humm.. how can I know that?
Will try a different SD card. One I know it's not class 6 and post tthe results here.

**macakinho** · May 11th, 2009

On a SD card I though would be way slower:

"1073741824 bytes (1.1 GB) copied, 117.218 s, 9.2 MB/s"

damn it, those cheecky ebayers...

**elitenoobboy** · August 23rd, 2009

Originally Posted by danwood76

Code:

dd count=1k bs=1M if=/dev/zero of=/media/HD2/test.img
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 7.69365 s, 140 MB/s

that command writes 1GB to the disk, this large number is because the filesystem on the device will speed up the transfer by caching the data if a small transfer is carried out.

If you use that command multiple times, is it normal for the speed to be lower on subsequent runs? The first time I ran it, creating a new file, test.img, I got 110MB/sec,* then each time after I run it, I get just under 50MB/sec. I changed to a different output file name, and the same thing happens, faster the first time at 114MB/s, then slower.

*the 110MB/sec is actually faster than what I get from the hdparm -t command: 90MB/s.

**TiloBunt** · September 1st, 2011

Originally Posted by danwood76

You can use DD to test disk speed, but it can easily lead to damaged data (partitions) if used incorrectly but is probably the most direct way of testing.

So for example my second internal disk is mount /media/HD2 so running this gives me the write speed:

Code:

dd count=1k bs=1M if=/dev/zero of=/media/HD2/test.img
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 7.69365 s, 140 MB/s

that command writes 1GB to the disk, this large number is because the filesystem on the device will speed up the transfer by caching the data if a small transfer is carried out.

--edit--
This is a VERY dangerous command if you miss-type the output file so obviously take care using it and be sure to type correctly!

Thanks for this info, works like a charm,

I played around with the 1k(1000 times) and 1M (1 Mb file) to test my 16 GB SD card.
Keep in mind FAT32 formated card only support single files (thats why the second one gave me a file too large.

Code:

tilo@t-laptop:/media/5E33-82DF$ dd count=1k bs=1M if=/dev/zero of=/media/5E33-82DF/test0.img
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 113.36 s, 9.5 MB/s
tilo@t-laptop:/media/5E33-82DF$ dd count=2k bs=4M if=/dev/zero of=/media/5E33-82DF/test1.img
dd: writing `/media/5E33-82DF/test.img': File too large
1024+0 records in
1023+0 records out
4294967295 bytes (4.3 GB) copied, 285.687 s, 15.0 MB/s
tilo@t-laptop:/media/5E33-82DF$ dd count=1k bs=3M if=/dev/zero of=/media/5E33-82DF/test2.img
1024+0 records in
1024+0 records out
3221225472 bytes (3.2 GB) copied, 246.827 s, 13.1 MB/s
tilo@t-laptop:/media/5E33-82DF$ dd count=1k bs=3M if=/dev/zero of=/media/5E33-82DF/test3.img
1024+0 records in
1024+0 records out
3221225472 bytes (3.2 GB) copied, 269.524 s, 12.0 MB/s
tilo@t-laptop:/media/5E33-82DF$ dd count=1k bs=3M if=/dev/zero of=/media/5E33-82DF/test4.img
1024+0 records in
1024+0 records out
3221225472 bytes (3.2 GB) copied, 268.86 s, 12.0 MB/s
tilo@t-laptop:/media/5E33-82DF$